GIFT  OF 

PROF.  W.B.  RISING 


APPLETONS' 
SCIENCE     TEXT-BOOKS. 


CHEMISTRY. 


SPKOTKA     OF  VARIOUS    SOimcKS    OK   LIGHT. 


The  Sun,.2.Tfi& 

9  .  Calcium 


ye.  .     . 
lQ.Sfjwn.tiu.ms.  H-Barium.  12 


6.  Caesium,. 


.  8  Th 


THE 


ELEMENTS  OF  CHEMISTRY. 


BY 
F.    W.    CLARKE, 

CHEMIST   OF  THE  UNITED   STATES   GEOLOGICAL   SURVEY. 


NEW  YORK: 

D.    APPLETON    AND    COMPANY, 

I,   3,    AND    5    BOND  STREET. 

1884. 


o 


COPYRIGHT,  1884, 
BY  D.  APPLETON  AND  COMPANY. 


PREFACE. 


IN  preparing  this  little  treatise  the  author  has 
had  several  objects  in  view.  First,  he  has  sought 
to  write  a  text-book  which  should  be  available  for 
use  with  elementary  classes,  and  in  which  the  diffi- 
culties of  chemical  science  should  be  encountered 
progressively,  rather  than  at  the  beginning.  Sec- 
ondly, he  has  considered  the  needs  of  those  stu- 
dents who,  while  anxious  to  learn,  are  unable  to 
secure  the  aid  of  a  teacher,  and  who,  therefore,  are 
obliged  to  study  by  themselves.  For  the  latter,  es- 
pecially, are  the  foot-note  references  to  other  works 
on  chemistry  ;  and  only  such  works  have  been  cited 
as  are  to  be  found  on  the  shelves  of  nearly  every 
well-equipped  public  library.  He  has  also  borne 
steadily  in  mind  the  fact  that  in  most  schools  there 
are  two  classes  of  students :  those  who  study  chem- 
istry merely  as  part  of  a  general  education,  without 
thought  of  going  further ;  and  those  who  are  likely 
in  time  to  take  a  more  advanced  course  of  chemi- 
cal training.  For  the  former  class  the  book  is  suffi- 

237513 


vi  PREFACE. 

ciently  full,  particularly  with  regard  to  the  every- 
day applications  of  chemistry  ;  for  the  second  class 
it  is  intended  to  serve  as  a  legitimate  scientific  basis 
for  subsequent  higher  study. 

The  value  of  a  school  text-book,  other  things 
being  equal,  depends  much  upon  the  use  made  of  it 
by  the  teacher.  In  his  hands  it  may  become  an 
instrument  for  developing  thought,  or  merely  a 
device  for  drilling  the  memory.  This  is  especially 
true  of  text-books  upon  -chemistry.  To  use  them 
properly  it  must  always  be  remembered  that  chem- 
istry is  essentially  a  disciplinary  study — as  much 
so  as  language  or  mathematics;  and  the  constant 
effort  of  the  teacher  should  be  to  train  the  pupil 
in  the  accurate  observation  of  phenomena,  and 
the  ability  to  draw  correct  conclusions  from  what 
he  sees.  Good  discipline  in  scientific  methods  of 
thought  must  always  be  kept  in  view  ;  and  this 
discipline  can  be  best  attained  by  simultaneous  drill 
in  the  facts  of  science  as  observed  in  the  lecture- 
room  or  laboratory,  and  in  the  philosophy  of  sci- 
ence which  is  reared  upon  them.  In  this  book 
the  effort  has  been  made  to  present,  as  a  rule, 
experimental  evidence  first  and  theoretical  discus- 
sions afterward ;  and  a  glance  at  the  chapters  upon 
atomic  weights,  formulae,  and  valency,  will  fairly 
illustrate  the  manner  in  which  this  purpose  has 
been  carried  out. 

Nearly  all  the  experiments  cited  in  this  volume 


PREFACE.  vii 

are  of  the  simplest  character.  The  greater  num- 
ber of  them  can  be  easily  performed  by  the  pupil 
himself,  with  no  more  complicated  apparatus  than 
can  be  improvised  from  such  common  materials  as 
are  everywhere  at  hand.  The  chemicals,  with  few 
exceptions,  are  inexpensive,  and  within  the  reach  of 
every  school ;  and,  although  a  good  laboratory  is 
desirable,  it  is  not  necessary  to  the  attainment  of 
really  substantial  results.  Every  experiment  should 
be  studied,  not  as  an  amusement,  but  for  what  it 
signifies  ;  and,  if  there  are  not  means  for  perform- 
ing it  just  as  it  is  described,  other  means  may  be 
readily  devised.  The  student  who  constructs  his 
own  apparatus  understands  its  meaning  much  bet- 
ter than  if  he  had  bought  a  far  more  elegant  outfit 
of  some  dealer. 

The  questions  and  exercises  at  the  end  of  the 
book  are  not  meant  to  be  exhaustive.  They  are 
merely  hints  to  aid  both  teacher  and  pupil  in  their 
work.  The  problems,  in  particular,  are  only  tenta- 
tive ;  some  classes  will  need  many  more  than  are 
given,  and  the  teacher  must  devise  such  as  will  be 
best  suited  to  circumstances. 

The  author's  acknowledgments  are  due  to  Miss 
Caroline  A.  Lord,  of  Cincinnati,  for  efficient  serv- 
ice in  the  preparation  of  a  considerable  number  of 
the  illustrations. 

WASHINGTON,  April,  1884. 


I 


TABLE  OF  CONTENTS. 


PART   I.— INORGANIC   CHEMISTRY. 

CHAP.  PAGE 

I.  INTRODUCTION       .        /      .       .      ,r       «       .        .      i 

II.  THE  CONSTITUTION  OF  MATTER.        ,       .,  ,     .        .      8 

III.  HYDROGEN    .        .        .        .        .       , '•"".•".      .        .    14 

IV.  OXYGEN 24 

V.  WATER 32 

VI.  NITROGEN  AND  THE  ATMOSPHERE       .        .        .        .49 

VII.  AMMONIA  AND  THE  OXIDES  OF  NITROGEN        .        .    55 

VIII.  ATOMIC  WEIGHTS  AND  CHEMICAL  FORMULAE     .        .    66 

IX.  CARBON  .        .     ' 74 

X.  CARBON  (continued) 90 

XI.  COMBINATION  BY  VOLUME 99 

XII.  VALENCY 105 

XIII.  THE  CHLORINE  GROUP in 

XIV.  THE  CHLORINE  GROUP  (continued)      .        .        .        .122 
XV.  SULPHUR .        .       .132 

XVI.  SULPHUR  (continued) 141 

XVII.  PHOSPHORUS 151 

XVIII.  ARSENIC,  BORON,  AND  SILICON 159 

XIX.  INTRODUCTORY  TO  THE  METALS         .        .        .        .172 
XX.  THE  METALS  OF  THE  ALKALIES         .        .        .        .183 

XXI.  SILVER  AND  THALLIUM 196 

XXII.  CALCIUM,  STRONTIUM,  AND  BARIUM     ....  205 

XXIII.  SPECTRUM  ANALYSIS 213 

XXIV.  GLUCINUM,  MAGNESIUM,  ZINC,  CADMIUM,  AND  MER- 

CURY       222 

XXV.  THE  ALUMINUM  GROUP 232 


TABLE  OF  CONTENTS. 

CHAP.  PAGE 

XXVI.  THE  TETRAD  METALS 239 

XXVII.  THE  ANTIMONY  GROUP .246 

XXVIII.  THE  CHROMIUM  GROUP.  253 

XXIX.  MANGANESE  AND  IRON.  262 

XXX.  NICKEL,  COBALT,  AND  COPPER 273 

XXXI.  GOLD,  AND  THE  PLATINUM  GROUP  ....  280 


PART   II.— ORGANIC   CHEMISTRY. 

XXXII.  PRELIMINARY  OUTLINE 285 

XXXIII.  CYANOGEN  AND  CARBONYL  COMPOUNDS  .        .        .  291 

XXXIV.  THE  METHANE  SERIES      .       .       .        .        .        .296 

XXXV.  THE  FATTY  ACIDS 303 

XXXVI.  THE  OLEFINES 310 

XXXVII.  GLYCERIN  AND  THE  FATS 316 

XXXVIII.  THE  CARBOHYDRATES 322 

XXXIX.  THE  BENZENE  DERIVATIVES 329 

XL.  THE  TERPENE,  CAMPHORS,  ALKALOIDS,  AND  GLU- 

COSIDES 338 

XLI.  ANIMAL  CHEMISTRY,  FERMENTATION        .        .        .  344 

APPENDIX    I.  COMPARATIVE  TABLE  OF  ENGLISH  AND  METRIC 

MEASURES,  THERMOMETRIC  RULES         ,        .351 
APPENDIX  II.  QUESTIONS  AND  EXERCISES 353 


PART     I. 

INORGANIC  CHEMISTRY. 


CHAPTER  I. 

INTROD  UCTION. 

WHEN  we  closely  observe,  the  occurrences  of 
Nature,  we  soon  see  that  two  great  classes  of 
changes  are  constantly  taking  place.  First,  there 
are  the  changes  which  do  not  affect  the  essential 
character  of  things :  like  the  motion  of  a  body  from 
one  spot  to  another,  and  the  variations  between  heat 
and  cold,  sound  and  silence,  light  and  darkness,  and 
so  on.  Secondly,  there  are  the  changes  which  sub- 
stances undergo  in  their  innermost  structure :  like 
the  transformation  of  wood  into  charcoal,  of  the  con- 
stituents of  soil  and  air  into  the  stems  and  leaves 
of  plants,  and  a  multitude  of  other  similar  altera- 
tions of  different  degrees  of  complexity.  Changes 
of  the  first  class  are  called  physical  changes,  while 
the  others  are  known  as  chemical;  and  it  is  with 
the  latter  that  the  science  of  chemistry  has  to  do. 

For  example,  a  piece  of  iron  may  be  converted 
into  a  magnet  and  afterward  deprived  of  its  mag- 
netic power,  thus  acquiring  and  losing  a  certain 
new  property  without  ceasing  to  be  metallic  iron. 
These  changes,  which  do  not  affect  the  nature  of 


the  metal  as  a  metal,  are  physical ;  and  so  also  are 
those  involved  in  raising  a  piece  of  the  iron  to  a  red 
heat,  or  in  rendering  it  fluid  by  melting.  But  if  the 
iron  be  placed  in  a  shallow  pool  of  water,  so  as  to 
be  partly  covered  and  partly  exposed  to  the  air,  it 
will  be  slowly  transformed  into  a  brownish-red  sub- 
stance called  rust,  and  here  the  alteration  is  chem- 
ical. The  iron  has  ceased  to  exist  as  iron,  and  has 
become  changed  into  something  quite  different. 
Again,  water  may  be  frozen  into  ice,  or  converted 
by  heat  into  steam ;  thus  showing  its  capacity  to 
exist  in  several  different  conditions,  without  ceasing 
to  be  the  same  substance.  These  changes,  there- 
fore, are  physical.  ,  But,  by  chemical  means,  the 
water  may  be  decomposed  into  two  gases — oxygen 
and  hydrogen — each  of  which  differs  widely  in  its 
properties  from  water,  and  neither  of  which  with- 
out the  other  can  reproduce  water.  This  trans- 
formation of  water  into  something  else  is  a  chemical 
transformation. 

The  following  experiments  will  serve  to  illus- 
trate chemical  changes: 

EXPERIMENT  i. — Rub  together  in  a  mortar  a 
small  quantity  of  copper -filings  with  half  their 
weight  of  sulphur.  No  matter  how  thoroughly  you 
mix  them,  you  can  still,  with  a  magnify  ing-glass, 
discern  the  separate  particles  of  the  two  substances. 
Now  insert  the  mixture  in  a  glass  tube  sealed  at  the 
lower  end,  and  heat  gently  over  a  flame.  Presently 
the  sulphur  will  melt,  and  shortly  afterward  the 
entire  mass  will  become  incandescent.  Upon  cool- 
ing, it  will  be  found  that  both  copper  and  sulphur 
have  disappeared,  and  in  their  place  is  a  grayish 
substance,  in  which  the  most  powerful  microscope 


INTRODUCTION.  3 

can  detect  no  particle  of  either  of  the  original 
bodies.  The  copper  and  sulphur  have  united  to 
form  a  new  substance,  known  as  copper  sulphide ; 


FIG.  i. — Union  by  Heat. 

and  thus  the  experiment  serves  to  illustrate  chemical 
combination.  It  also  teaches  the  difference  between 
chemical  combination  and  mere  mechanical  mixture. 
Instead  of  copper,  iron  may  be  used  in  this  experi- 
ment, and  then  iron  sulphide  will  be  formed.  Be- 
fore heating,  the  metal  may  be  separated  from  the 
sulphur  by  means  of  a  magnet ;  but  after  union  has 
taken  place  the  iron  can  not  be  thus  withdrawn. 

EXPERIMENT  2. — Place  in  a  dry  test-tube  a  lit- 
tle red  mercuric  oxide,  and  heat  cautiously  over  a 
flame.  Soon  globules  of  metallic  mercury  or  quick- 
silver will  be  seen  in  the  bottom  of  the  tube,  or  con- 
densed upon  its  cooler  sides.  In  the  tube  there  will 
also  be  a  quantity  of  oxygen  gas,  which  may  be 
recognized  by  the  fact  that  a  kindled  match  will 
burn  more  brilliantly  in  it  than  in  the  outer  air. 


4  INORGANIC  CHEMISTRY. 

The  original  red  substance  has  been  divided  into 
two  substances,  a  gas  and  a  metal ;  so  that  here  we 
have  an  instance  of  chemical  decomposition.* 

EXPERIMENT  3. — Rub  together  in  a  mortar  a  lit- 
tle potassium  iodide  and  a  little  mercuric  chloride. 
Presently,  in  place  of  the  two  white  substances,  a 
scarlet  powder  will  appear.  This  chemical  change 
is  more  complicated  than  either  of  the  foregoing 
cases,  and  is  an  instance  of  double  decomposition. 
Here  two  compounds  exchange  their  constituents, 
each  decomposing  the  other,  new  compounds  at  the 
same  time  being  formed.  This  phase  of  action  will 
be  considered  more  fully  in  another  chapter. 

In  several  ways  these  experiments  are  instructive. 
They  show,  for  example,  how  wonderfully  a  chem- 
ical change  affects  the  physical  properties  of  things, 
the  properties  of  a  compound  being  often  widely 
different  from  those  of  the  substances  which  have 
united  to  produce  it.  Under  proper  conditions, 
black,  tasteless,  odorless  charcoal  may  be  made  to 
unite  with  yellow,  tasteless,  odorless  sulphur;  the 
product  of  the  union  of  these  two  solids  being  a 
volatile,  colorless,  transparent  liquid,  with  a  nau- 
seous odor  and  burning  taste.  A  more  complete 
transformation  can  hardly  be  imagined. f 

It  will  be  observed  that  in  two  of  the  foregoing 

*  Copper  formate  is  even  better  than  mercuric  oxide  for  strikingly 
illustrating  decomposition.  When  heated  in  a  tube  the  brilliant  blue 
crystals  evolve  gas  copiously,  and  pure  metallic  copper  remains  behind. 
The  substance  may  be  prepared  by  dissolving  copper  oxide  in  warm 
formic  acid,  and  aHowing  the  solution  to  crystallize.  Unfortunately, 
the  materials  are  not  readily  available  in  all  school  laboratories. 

f  At  this  point  the  teacher  will  do  well  to  show  the  class,  side  by 
side,  a  fragment  of  charcoal,  a  bit  of  sulphur,  and  a  bottle  of  carbon 
disulphide. 


INTRODUCTION.  5 

experiments  heat  is  applied:  in  one  case  as  a  de- 
composing agent,  in  the  other  as  a  means  of  caus- 
ing union.  Another  experiment  will  bear  advanta- 
geously upon  these. 

EXPERIMENT  4. — Pulverize,  in  a  perfectly  clean 
mortar,  a  little  potassium  chlorate.  Transfer  it  to  a 
sheet  of  paper,  and  mix  carefully  with  it,  without 
rubbing,  an  equal  quantity  of  powdered  sugar.  Place 
the  mixture  where  no  harm  can  be  done,  and  drop 
upon  it,  from  a  glass  rod,  a  single  drop  of  strong 
sulphuric  acid.  The  mass  will  immediately  catch 
fire,  burning  with  almost  explosive  violence,  and 
with  a  peculiar  rose-colored  flame.  Here,  then,  we 
have  a  chemical  change  which  produces  a  great 
amount  of  heat. 

We  now  see  that  heat  plays  a  very  important 
part  in  chemical  changes ;  and,  as  we  go  on,  we 
shall  find  that  other  agencies,  such  as  light,  elec- 
tricity, etc.,  are  also  often  involved.  In  order, 
then,  that  a  chemical  change  may  be  completely 
understood,  three  things  have  to  be  studied,  as 
follows : 

First,  the  properties  of  the  substances  entering 
into  the  change.  Secondly,  the  physical  phenomena 
occurring  during  the  change.  Thirdly,  the  prop- 
erties of  the  substances  which  result  from  the 
change. 

In  such  investigations  one  principle,  which  un- 
derlies all  science,  must  be  steadily  kept  in  view. 
In  no  case  is  anything,  either  matter  or  force,  ever 
created  or  destroyed.  By  matter  is  meant  any- 
thing which  occupies  space  and  possesses  weight : 
like  iron,  wood,  water,  or  air.  By  force  is  under- 
stood any  agency  capable  of  producing  motion,  or 


6  INORGANIC  CHEMISTRY. 

of  altering  the  direction  of  a  moving  body  ;  *  and  such 
things  as  heat,  light,  electricity,  mechanical  power, 
etc.,  are  called  forces.  When  two  bodies  act  upon 
each  other  chemically,  they  do  so  under  the  influence 
of  a  peculiar  force,  known  variously  as  chemical 
affinity,  chemical  attraction,  or,  more  briefly,  chem- 
ism.  When  two  substances  unite,  it  is  this  force 
which  brings  them  together ;  when  they  are  separat- 
ed, this  force  has  to  be  overcome.  In  consequence, 
every  chemical  change  involves  some  transformation 
of  force,  but  none  is  ever  created  or  destroyed.  So 
also  with  the  matter  changed :  however  complicated 
its  alteration  may  be,  no  particle  is  ever  lost,  no  new 
particle  ever  appears.  When  a  candle  is  burned,  a 
series  of  chemical  changes  takes  place.  Heat  is  de- 
veloped by  chemical  action,  and  a  certain  amount  of 
matter  seems  to  disappear.  But,  if  all  the  products 
of  combustion,  solid  or  gaseous,  be  collected  and  accu- 
rately weighed,  it  will  be  found  that  nothing  has  real- 
ly vanished.  The  matter  of  the  candle  and  of  the  air 
in  which  it  burned  have  acted  upon  each  other  chem- 
ically, and  new  substances  have  been  formed ;  but 
neither  destruction  nor  creation  of  matter  was  possi- 
ble. It  is  with  the  transformations  of  matter,  its  combi- 
nations and  decompositions,  that  the  chemist  has  to  deal. 
In  the  light  of  the  foregoing  pages  we  may  now 
frame  an  intelligible  definition,  as  follows  :  Chemistry 
is  the  science  which  investigates  the  composition  of  sub- 
stances, together  with  the  combinations  and  decomposi- 
tions resulting  from  their  action  upon  one  another  under 
the  influence  of  chemical  force.\ 

*  For  more  exhaustive  definitions,  the  works  on  mechanics  and 
physics  may  be  consulted. 

f  The  essential  features  of  this  definition  may  be  expressed  in  a 


INTRODUCTION.  j 

At  the  beginning  of  any  study  the  question  of 
utility  is  apt  to  arise.  With  chemistry  the  answer 
to  this  question  is  twofold  :  First,  its  value  as  an 
educational  instrument,  as  a  means  of  mental  dis- 
cipline, is  very  great.  Secondly,  its  material  advan- 
tages are  enormous.  The  discoveries  of  chemists 
are  now  applied  to  practical  use  in  agriculture,  in 
medicine,  and  in  every  great  manufacturing  indus- 
try. By  the  help  of  chemistry  many  substances 
which  were  formerly  wasted  are  now  rendered  use- 
ful. For  example,  from  coal-tar  the  most  brilliant 
dyes  are  made.  Our  dwellings  are  now  lighted 
with  chemically  refined  oil  and  candles,  or  by  chem- 
ically made  gas ;  and  these  are  kindled  with  matches 
which  chemistry  has  given  us  in  place  of  the  old 
flint  and  steel.  Our  clothing  is  bleached  or  dyed 
by  chemical  means ;  metals  are  extracted  from  their 
ores  by  chemical  processes ;  soap,  glass,  porcelain, 
paints,  varnishes,  etc.,  have  all  become  better  and 
cheaper  than  before  the  chemist  studied  them.  Bar- 
ren soil  is  now  rendered  fruitful  by  chemical  fer- 
tilizers ;  wood  is  preserved  from  decay  by  chemical 
applications ;  diseases  are  checked  by  chemical  dis- 
infectants ;  and  a  multitude  of  chemical  preparations 
aid  the  physician  in  alleviating  pain. 

variety  of  other  ways.  The  pupil  will  find  it  a  useful  exercise  to  ar- 
range other  definitions,  so  as  to  see  the  subject  from  several  different 
points  of  view. 


CHAPTER   II. 

THE  CONSTITUTION   OF   MATTER. 

IN  order  to  determine  the  composition  of  any 
substance,  the  chemist  may  resort  to  two  distinct 
methods,  analysis  and  synthesis.  By  analysis,  a  body 
is  separated  into  its  component  parts,  which  are  then 
identified.  By  synthesis  these  parts  may  be  artifi- 
cially combined,  so  as  to  produce  the  substance 
under  investigation.  For  example,  the  composition 
of  water  may  be  ascertained  by  dividing  it  into  its 
two  constituents,  oxygen  and  hydrogen ;  or  it  may 
be  determined  by  causing  these  gases  to  unite,  and 
proving  that  by  their  union  water  is  actually  formed. 
Each  method  re-enforces  the  other,  and  strengthens 
the  final  conclusion. 

In  Nature  the  chemist  recognizes  an  almost  limit- 
less number  of  different  substances,  the  composition 
of  which  he  tries  to  discover  by  either  or  both  of 
the  above  methods.  Besides,  he  has  to  deal  with 
vast  numbers  of  artificial  bodies ;  of  which  so  many 
are  theoretically  possible  that  infinity  would  barely 
suffice  to  express  them.  In  the  analysis  of  all  these 
substances,  however,  he  finds  the  same  component 
parts  continually  repeated  in  various  modes  of  un- 
ion ;  and  he  finally  arrives  at  bodies  so  simple  that 
they  can  not  be  analyzed  further.  These  simple 


THE  CONSTITUTION  OF  MATTER. 


9 


substances,  of  which  at  present  some  seventy  are 
known,  he  terms  elements.  All  other  substances, 
which  are  formed  by  the  chemical  union  of  elements 
with  each  other,  and  which  are  consequently  sepa- 
rable into  elements  by  analysis,  he  calls  compounds. 
Thus,  the  oxygen  and  hydrogen  previously  referred 
to  are  elements,  for  by  no  means  within  the  chem- 
ist's control  can  they  be  decomposed  into  simpler 
bodies ;  while  the  water  formed  by  their  union  is 
a  compound,  and  is  said  to  be  composed  of  these 
elements.  The  following  table  contains  a  list  of  all 
the  elements  now  known.  The  use  of  the  "  sym- 
bols" and  the  meaning  of  the  "atomic  weights" 
will  be  explained  further  on.  New  elements  are 
occasionally  discovered,  usually  as  constituents  of 
very  rare  minerals. 

Table  I. — Elements,  Symbols,  and  Atomic  Weights. 


NAME. 

Symbol. 

Atomic 
weight. 

NAME. 

Symbol. 

Atomic 
weight. 

Aluminum 

Al. 

27. 

Erbium  

Er. 

1  66. 

Antimony  

Sb. 

120. 

FLUORINE  

F. 

19. 

ARSENIC 

As. 

75. 

Gallium 

Ga. 

69. 

jBarium 

Ba. 

I?7. 

Glucinum  

Gl. 

9- 

Bismuth 

Bi 

->o8 

Gold. 

Au. 

196.5 

BORON  

B. 

1  1. 

v  HYDROGEN  .  .  . 

H. 

i. 

^BROMINE 

Br. 

80. 

Indium  

In. 

113.6 

Cadmium 

Cd 

112. 

V!ODINE 

I. 

127. 

CcCsium 

Cs. 

J-2  •J. 

Iridium  

Ir. 

193. 

Calcium 

Ca 

'    4.O 

Iron 

Fe. 

f 

56. 

"CARBON  

C. 

12. 

Lanthanum  .... 

La. 

138.2 

CERIUM 

Ce 

T/1T 

Lead 

Pb. 

207. 

^CHLORINE 

Cl 

•2C    C 

Lithium  

Li. 

7. 

Chromium  

Cr. 

C2. 

Magnesium  .... 

Mg. 

24. 

Cobalt 

Co. 

CQ 

Manganese  .... 

Mn. 

cc. 

Columbium 

Cb 

QA 

Mercury 

HP- 

2OO. 

Conner  .  . 

Cu. 

5a 

Molybdenum  .  . 

Mo. 

96. 

X  *?  . 

Decipium 

Dp. 

>3 

Nickel  

Ni. 

58. 

Didvmium  .  . 

DL 

14.2.1 

^NITROGEN  .  . 

N. 

14.. 

10 


INORGANIC  CHEMISTRY. 


NAME. 

Symbol. 

Atomic 
weight. 

NAME. 

Symbol. 

Atomic 
weight. 

—Osmium  . 

Os. 
0. 
Pd. 
P. 
Pt. 
K. 
Rh. 
Rb. 
Ru. 
Sm. 
Sc. 
Se. 
Si. 
Ag. 
Na. 
Sr. 

199.? 

1  6. 
106. 

31- 
195. 

39- 
104. 

85.5 
104. 
150. 

44. 

79- 
28. 
108. 

£5 

\i>ULPHUR 

S. 
Ta. 
Te. 
Tb. 
Tl. 
Th. 
Tm. 
Sn. 
Ti. 
W. 
U. 
V. 
Yt. 
Yb. 
Zn. 
Zr. 

32. 
IS2.6 
126.  ? 
? 
204. 

23|- 

118. 
48. 
184. 

239- 

^ 

173- 
65. 
90. 

OXYGEN. 

Tantalum  . 

Palladium  

TELLURIUM... 
Terbium  

^PHOSPHORUS... 
Platinum. 

Thallium 

Potassium  

Thorium  

Rhodium  . 

Thulium 

Rubidium  ,  . 

Tin  

Ruthenium 

Titanium  
Tungsten 

Samarium  .. 

Scandium  

Uranium  

SELENIUM 

Vanadium  . 

SILICON  . 

Yttrium  

Ytterbium  

Sodium  . 

Zinc 

Strontium  

Zirconium  

Of  these  elements  by  far  the  greater  number  are 
metallic ;  like  gold,  iron,  zinc,  etc.  A  smaller  num- 
ber, given  in  the  table  in  small  capitals,  are  called 
non-metallic ;  and  of  these  carbon,  oxygen,  and  sul- 
phur are  good  examples.  In  the  subsequent  chap- 
ters the  latter  class  of  elements  will  be  studied  first. 
Between  the  metals  and  the  non-metals,  however, 
no  sharp  distinctions  can  be  drawn;  arsenic,  for 
example,  may  be  fairly  put  in  either  class;  the 
division,  therefore,  is  mainly  one  of  convenience, 
and  is  not  fundamentally  important. 

In  order  that  we  may  be  able  to  account  for 
many  of  the  properties  of  matter,  we  must  study 
its  physical  constitution  still  more  closely.  Take, 
for  example,  a  piece  of  iron :  when  it  is  heated,  it 
expands,  and  occupies  more  space  than  before ; 
when  cooled,  it  contracts  and  becomes  smaller ;  al- 
though in  both  cases  the  weight  remains  the  same. 


THE  CONSTITUTION  OF  MATTER.  u 

Weight,  therefore,  may  be  regarded  a  constant 
property  of  matter,  while  volume  or  bulk  is  vari- 
able. This  variability  in  volume  is  most  easily  ac- 
counted for  upon  the  supposition  that  matter,  as  we 
ordinarily  recognize  it,  is  made  up  of  minute,  sepa- 
rate particles,  which  may  be  driven  farther  apart  or 
crowded  closer  together  by  various  means.  These 
particles  the  physicist  terms  molecules,  and  they  are 
considered  to  be  by  all  mechanical  means  indivisi- 
ble. Every  kind  of  matter  is  built  up  of  its  own 
characteristic  kind  of  molecules ;  these  are  exactly 
alike,  although  different  from  the  molecules  of  every 
other  substance,  and  they  are  separated  by  larger  or 
smaller  spaces.  They  are  furthermore  supposed  to 
be  in  more  or  less  rapid  motion ;  and  upon  this  sup- 
position the  mathematical  theories  of  heat  and  elec- 
tricity are  very  largely  based.  Of  course,  molecules 
are  exceedingly  small — so  small  that  we  may  never 
be  able  to  see  or  handle  them  experimentally.  There 
are,  however,  abundant  reasons  for  asserting  their 
existence ;  and  it  is  even  possible  to  calculate  from 
physical  data  something  approximate  concerning 
their  size.  Evidence  can  be  drawn  from  several 
sources  showing  that  about  five  hundred  millions  of 
hydrogen-molecules,  placed  in  a  row,  would  only 
form  a  line  an  inch  long ;  or,  in  other  words,  there 
are  about  two  hundred  millions  to  the  linear  centi- 
metre.* 

But,  although  molecules  are  mechanically  indi- 
visible, by  chemical  means  we  can  divide  them  into 
smaller  particles  still.  For  example,  a  drop  of  water 

*  For  fuller  details,  consult  Tait's  "  Recent  Advances  in  Physical 
Science,"  chapters  xii  and  xiii ;  also  Cooke's  "  New  Chemistry,"  pp. 
27-36. 


12  INORGANIC  CHEMISTRY. 

may  be  divided  and  subdivided  until  the  molecules 
of  water  are  reached ;  and  each  of  these  will  still 
possess  all  the  properties  of  water.  But  water  is  a 
compound  of  two  elements,  oxygen  and  hydrogen ; 
and  therefore  every  one  of  its  molecules  may  be 
decomposed  into  these  two  substances.  The  smaller 
portions  of  oxygen  and  hydrogen  thus  recognized 
are  called  atoms.  The  molecule  of  any  chemical 
compound,  then,  is  a  cluster  of  atoms ;  and  it  is  only 
between  atoms  that  the  force  of  chemical  attraction 
comes  into  play.  In  future  chapters  some  of  the 
properties  of  atoms  will  be  considered.  For  pres- 
ent purposes  the  following  definitions  will  be  found 
useful : 

A  mass  of  matter  is  any  portion  of  matter 
which  can  be  recognized  by  the  senses.  Every 
mass  is  an  aggregation  of  molecules.  Masses  at- 
tract each  other  by  the  force  of  gravitation.  The 
science  of  mechanics  deals  with  masses  and  their 
motions. 

A  molecule  is  the  smallest  particle  of  any  sub- 
stance which  can  exist  in  the  free  state,  and  in 
which  the  characteristic  properties  of  the  sub- 
stance are  retained.  It  is  also  the  smallest  por- 
tion of  matter  which  can  take  part  in  any  phy- 
sical change.  The  science  of  molecular  physics 
(including  heat,  light,  and  electricity)  deals  large- 
ly with  molecules  and  their  motions.  Nearly  all 
molecules  are  clusters  of  atoms;  but,  for  a  very 
few  substances,  the  molecule  and  the  atom  are  the 
same. 

An  atom  is  the  smallest  quantity  of  any  substance 
which  can  enter  into  chemical  union,  or  take  part 
in  any  chemical  change.  Chemistry  may  be  defined 


THE  CONSTITUTION  OF  MATTER.  ^ 

as  the  science  which  treats  of  atoms  and  their  at- 
tractions for  each  other.* 

*  This  definition  may  be  considered  as  a  supplement  to  the  one 
given  in  the  preceding  chapter.  The  subject  of  atoms  and  molecules 
may  be  read  up  to  advantage  in  Cooke's  "  New  Chemistry,"  Wurtz's 
"  Atomic  Theory,"  Cooke's  "  Chemical  Philosophy,"  or  Remsen's 
"  Theoretical  Chemistry." 


CHAPTER   III. 

HYDROGEN. 

IN  the  preceding  chapters  reference  has  been 
made  to  the  fact  that  water  is  composed  of  hydro- 
gen and  oxygen.  We  may  now  study  hydrogen, 
oxygen,  and  water  separately  and  in  detail. 

Hydrogen,  although  it  had  been  obtained  and 
partly  examined  by  several  earlier  investigators, 
was  first  accurately  studied  by  Cavendish  in  1766. 
In  1781  he  made  the  additional  discovery  that  water 
is  the  only  product  of  its  combustion ;  and,  on  ac- 
count of  this  fact,  Lavoisier  gave  it  its  present  name, 
which  signifies  "  water-producer."  It  may  be  easily 
obtained  from  water  as  follows : 

EXPERIMENT  5. — Wrap  a  bit  of  sodium  as  large 
as  a  pea  in  some  wire-gauze,  and  hold  it  by  a  handle 
of  stout  wire  under  the  mouth  of  an  inverted  test- 
tube  filled  with  water  in  a  pneumatic  trough.  In- 
stead of  the  latter  piece  of  apparatus,  a  common, 
deep  earthenware  dish  full  of  water  may  be  used. 
The  test-tube  should  be  filled  with  water  completely  ; 
then,  by  closing  its  mouth  with  the  thumb,  it  may 
be  inverted  and  placed  easily  in  position.  The  so- 
dium will  at  once  be  attacked  by  the  water,  bubbles 
of  gas  will  be  evolved  and  rise  into  the  tube,  and  soon 
the  latter  will  be  full.  Again  close  the  mouth  of 


HYDROGEN. 


the  tube  with  the  thumb,  and  bring  it  mouth  upper- 
most. Now,  upon  removing  the  thumb,  and  in- 
stantly applying  a  match,  the  gas  in  the  tube  will 


FIG.  2. — Preparation  of  Hydrogen  with  Sodium. 

ignite,  and  burn  with  a  pale,  bluish  flame.  The  gas 
is  hydrogen.  Since  the  bit  of  sodium  may  produce 
a  slight  explosion,  it  is  prudent  in  this  experiment 
to  wear  stout  gloves. 

In  the  foregoing  experiment  the  sodium  with- 
draws oxygen  from  the  water,  setting  hydrogen 
free.  When  steam  is  passed  through  a  gun-barrel 
or  piece  of  gas-pipe  filled  with  iron-filings  and  heated 
to  redness,  a  similar  change  takes  place  ;  the  oxygen 
of  the  steam  being  retained  by  the  iron,  so  that  only 
hydrogen  escapes  at  the  farther  end  of  the  appa- 
ratus. But,  for  preparing  hydrogen  in  quantity,  the 
subjoined  method  is  the  most  convenient  : 

EXPERIMENT  6. — Place  a  quantity  of  granulated 
zinc  (prepared  by  pouring  melted  zinc  from  a  height 
of  three  or  four  feet  into  cold  water)  in  a  gas  deliv- 
ery-flask (Fig.  3),  and  cover  it  with  dilute  hydro- 
chloric acid.  Iron-filings  may  be  used  instead  of 
zinc,  and  sulphuric  acid  in  place  of  hydrochloric.* 

*  Some  druggists  and  dealers  in  chemicals  still  retain  for  this  acid 
the  nearly  obsolete  name  of  muriatic  acid. 
2 


i6 


INORGANIC  CHEMISTRY. 


In  either  case  hydrogen  will  be  copiously  evolved ; 
and  it  may  be  collected  over  water  in  a  number  of 
small,  wide-mouthed  bottles.  The  first  portions  of 
gas  should  be  allowed  to  escape,  since  they  will  be 


FIG.  3.  — Preparation  of  Hydrogen. 

contaminated  with  the  air  which  originally  filled 
the  apparatus.  By  applying  a  flame  to  the  mouth 
of  one  of  the  little  bottles,  the  inflammability  of  hy- 
drogen may  again  be  recognized. 

Hydrogen,  when  perfectly  pure,  is  a  colorless, 
tasteless,  odorless  gas.  As  ordinarily  prepared,  how- 
ever, it  is  apt  to  be  disagreeably  scented  by  impuri- 
ties derived  from  the  materials  used  in  its  manufac- 
ture. It  is  found  in  Nature,  in  the  free  state,  among 
the  gases  exhaled  by  certain  volcanoes ;  and  it  is 
also  contained  in  many  meteoric  irons.  Not  only 
iron,  but  several  other  metals  also,  notably  palla- 
dium, have  the  property  of  absorbing  (or  occluding) 


HYDROGEN.  17 

considerable  quantities  of  hydrogen.  Since  metals 
containing  occluded  hydrogen  exhibit  in  some  de- 
gree the  properties  of  alloys,  it  has  been  suggested 
that  hydrogen  ought  to  be  classed  as  a  metal  also ; 
and  some  chemical  reasons,  which  will  be  cited 
further  on,  tend  to  support  this  view.  Hydrogen 
exists  in  enormous  quantities  in  the  atmosphere  of 
the  sun,  and  in  most  of  the  other  self-luminous 
heavenly  bodies,  its  presence  there  being  revealed 
to  us  by  the  spectroscope.  It  is  an  important  con- 
stituent of  coal-gas ;  and  in  the  combined  state  we 
find  it  not  only  in  water,  but  in  nearly  all  animal 
and  vegetable  substances,  in  petroleum,  and  in  a 
great  many  artificial  products. 

We  have  already  seen  that  hydrogen  is  inflam- 
mable, and  that  its  flame  is  but  feebly  luminous.  It 
is,  however,  exceedingly  hot,  as  the  following  ex- 
periment will  show : 


FIG.  4. — Combustion  of  Hydrogen. 

EXPERIMENT  7. — Generate  hydrogen  as  in  Ex- 
periment 6 ;  only,  instead  of  collecting  it  over  water, 


1 8  INORGANIC  CHEMISTRY. 

allow  it  to  issue  into  the  air  through  a  long  glass 
tube  drawn  out  to  a  fine  jet  at  the  end.  Allow  the 
gas  to  escape  for  some  time,  until  all  the  air  origi- 
nally contained  in  the  flask  has  been  expelled ;  then 
light  the  jet  of  gas  and  observe  the  character  of  the 
flame.  Now  insert  in  the  flame  a  little  fine  coil  of 
platinum  wire.  It  will  at  once  become  brilliantly 
white-hot  If  the  gas  is  kindled  while  air  remains  in 
the  flask,  a  violent  explosion  will  ensue.  By  holding 
a  cold  test-tube  inverted  over  the  hydrogen-flame, 
the  formation  of  drops  of  water  as  a  product  of  com- 
bustion may  be  observed. 

Hydrogen  is  incapable  of  supporting  respira- 
tion ;  hence,  small  animals  immersed  in  it  soon  die. 
The  pure  gas  may,  however,  be  inhaled  to  a  limited 
extent  without  danger.  When  the  lungs  are  filled 
with  it,  even  the  gruffest  voice  becomes  curiously 
shrill  and  hollow. 

Hydrogen  is  the  lightest  of  all  known  substances. 
Hence  its  use  in  the  filling  of  balloons,  although  for 
this  purpose  coal-gas  is  now  more  generally  em- 
ployed. 

EXPERIMENT  8. — Collect  the  hydrogen  from  a 
generating-flask  in  a  large  bladder,  and,  when  the 
latter  is  full,  tie  it  tightly  around  the  neck  with 
string.  An  inexpensive  toy-balloon  is  thus  made. 

EXPERIMENT  9. — Fill  a  small  india-rubber  gas- 
bag with  hydrogen,  and  attach  a  clay  tobacco-pipe 
to  its  nozzle  by  a  bit  of  rubber  tube.  The  pipe 
may  now  be  used  for  blowing  soap-bubbles,  which 
are  filled  with  hydrogen  by  a  gentle  pressure  on 
the  bag.  The  bubbles  rise  at  once  to  the  ceil- 
ing, on  account  of  their  remarkable  lightness. 
By  touching  each  bubble  with  a  candle-flame,  the 


HYDROGEN. 


inflammability  of  hydrogen  may  be  further  illus- 
trated. 

EXPERIMENT  10.  —  Hydrogen  may  be  poured 
from  one  bottle  into  another,  but  it  must  be  poured 
upward.  One  of  the  small 
bottles  filled  in  Experiment 
6  will  do  for  this  experi- 
ment. When  the  gas  has 
been  transferred,  it  may  be 
recognized  in  the  second 
bottle  by  its  inflammability. 
(See  Fig.  5.) 

The  weight  of  one  litre 
(or  cubic  decimetre)  of  hy- 
drogen, measured  at  the 
temperature  of  o°  centi- 
grade, and  under  a  baro- 
metric pressure  of  760  mil- 
limetres, is  only  0.0896  gramme.*  This  weight  is 
called  a  crith,  and  is  an  important  unit  of  weight 
in  all  gas  calculations.  In  the  subjoined  table  it  is 
compared  with  the  weight  of  equal  bulks  of  air, 
water,  and  platinum — the  latter  being  the  heaviest 
substance  known. 

One  cubic  decimetre  of  hydrogen  weighs  0.0896  gramme. 
"  air  "          1.2932 

"          water         "     1000.0000  grammes. 
<4  "  platinum     "  21500.0000        " 

Hence,  air  is  14.43  times,  water  a  little  over  11,000 
times,  and  platinum  about  240,000  times  heavier  than 
hydrogen. 

In  many  chemical  calculations  the  volume  occu- 

*  Tables  of  metric  weights  and  measures,  and  of  the  different  ther- 
mometric  scales,  may  be  found  in  the  Appendix. 


FIG.  5. — Pouring  Hydro- 
gen up. 


20  INORGANIC  CHEMISTRY. 

pied  by  a  given  quantity  of  gas  is  a  very  important 
factor.  Since  the  volume  of  a  gas  depends  upon 
conditions  of  temperature  and  pressure,  we  must 
take  these  agencies  into  account,  and,  for  conven- 
ience, we  must  first  establish  some  definite  standards 
of  comparison.  The  normal,  or  standard,  tempera- 
ture is  assumed  to  be  o°  centigrade,  or  32°  Fahren- 
heit. The  normal  atmospheric  pressure  is  indicated 
by  the  barometer  when  the  mercurial  column  is 
exactly  760  millimetres  high.  Volumes  of  gases, 
then,  are  always  to  be  compared  at  o°  centigrade, 
and  under  760  millimetres  pressure  ;  and,  whenever 
they  have  been  measured  under  other  conditions,  it 
is  customary  to  reduce  them  to  these  standards. 

The  law  governing  the  expansion  of  gases  by 
heat  is  very  simple.  For  present  purposes  it  may 
be  stated  thus  :  All  gases  expand  equally  for  equal  rises 
of  temperature.  Although  this  is  only  approximately 
true,  its  variations  from  absolute  accuracy  need  not 
be  considered  in  ordinary  calculations.  The  errors 
introduced  are  so  small  that  they  may  be  safely 
ignored ;  just  as  in  measuring  the  width  of  a  room  a 
thousandth  of  an  inch  more  or  less  counts  for  nothing. 
For  each  degree  centigrade,  a  gas,  measured  origi- 
nally at  o°,  will  expand  -^  of  its  bulk  ;  thus : 


273  volumes  of  air  at  o°  become — 

274  «        at        i°, 
275 

276 

273  +  t 

272 

271         '         "    —2°,  etc. 

If  this  rule  were  absolutely  true,  then,  at  273°  be- 
low zero,  the  volume  of  a  gas  would  become  nothing, 


HYDROGEN.  21 

and  matter  would  absolutely  vanish.  Accordingly, 
273°  below  the  centigrade  zero  is  called  the  absolute 
zero  of  temperature.  Of  course,  this  value  has  no  ex- 
perimental meaning,  since  it  can  never  be  reached  : 
but  it  has  some  mathematical  importance.  Gases 
cease  to  be  gases,  and  condense  to  liquids  or  solids, 
long  before  reaching  so  low  a  temperature. 

Suppose,  now,  we  have  two  volumes  (two  litres, 
or  two  cubic  feet,  or  whatever  units  you  please)  of 
hydrogen  at  o°,  and  wish  to  calculate  what  its  bulk 
would  be  if  heated  up  to  25°.  The  formula  is  as 
follows : 

273  :  273  +  25  ::  2  :  x. 

Conversely,  if  we  measure  two  volumes  at  25°,  and 
wish  to  reduce  it  to  o° : 

273  +  25  :  273  ::  2  :  x. 

Again,  let  us  take  twelve  volumes  of  gas  at  37°,  and 
wish  to  determine  its  volume  after  cooling  to  23° : 

273  +  37  :  273  +  23  ::  12  :  x. 

In  some  cases  we  have  to  deal  with  volumes  of 
gases  below  o°.  Then,  instead  of  adding,  we  sub- 
tract the  given  number  of  degrees  from  the  stand- 
ard volume,  273.  In  short,  we  always  express  the 
volume  of  a  gas  at  o°  by  273,  assume  an  increase  or 
decrease,  as  the  case  may  be,  for  each~degree  of 
difference  from  o°,  and  then,  by  a  simple  propor- 
tion, the  reduction  to  o°  may  be  easily  made.* 

The  changes  in  the  volume  of  a  gas  due  to  va- 

*  Most  of  the  problems  which  arise  in  chemical  calculations  are 
most  clearly  and  logically  stated  in  the  form  of  simple  proportions. 
Every  pupil  should,  therefore,  become  accustomed  to  this  method  of 
computing. 


22  INORGANIC  CHEMISTRY. 

nations  in  pressure  are  governed  by  a  very  simple 
law,  as  follows  :  The  volume  of  a  gas  is  inversely  pro- 
portional to  the  pressure.  This  is  termed  the  law  of 
Boyle  and  Marriotte,  having  been  independently  dis- 
covered by  these  two  investigators.  If  we  double 
the  pressure  under  which  a  gas  is  kept,  we  halve  its 
volume ;  if  we  halve  the  pressure,  we  double  the 
volume,  and  so  on.  This  relation  is  conveniently 
expressed  by  the  formula  P,  :  P : :  V  :  Vx ;  in  which 
V  represents  the  volume  under  the  pressure  P,  and 
Vj  the  volume  under  the  altered  pressure  P,.  For 
example,  suppose  we  have  measured  ten  volumes  of 
hydrogen  when  the  barometer  stood  at  771  milli- 
metres, and  we  wish  to  calculate  what  it  would  be- 
come at  760  millimetres : 

760  :  771  ::  10  :  x. 

Here  we  see  that,  under  the  lower  pressure,  the  gas 
has  expanded  slightly.  Conversely,  if  ten  volumes 
have  been  measured  at  760  millimetres,  they  will 
become  less  than  ten  at  771  millimetres,  thus: 

771  :  760  ::  10  :  x. 

The  law  governing  pressures  is,  like  that  relating 
to  temperatures,  only  a  very  close  approximation  to 
the  truth.  Its  variations  from  accuracy  can,  how- 
ever, only  be  detected  by  the  most  refined  experi- 
ments.* 

By  intense  cold  and  great  pressure  all  gases  are 
condensible  to  liquids,  and  even  into  the  solid  state. 
For  hydrogen,  this  was  first  experimentally  accom- 

*  The  experimental  evidence  for  these  laws  may  be  read  up  in  a 
volume  upon  physics.  A  good  theoretical  discussion  of  them  may  be 
found  in  the  third  chapter  of  Cooke's  "  Chemical  Philosophy,"  new 
edition. 


HYDROGEN.  23 

plished  by  MM.  Cailletet  and  Pictet  (working  inde- 
pendently of  each  other)  at  the  close  of  the  year 
1877.  By  Pictet  it  was  cooled  to  —140°  centigrade 
under  a  pressure  of  650  atmospheres.  (The  press- 
ure exerted  by  the  air  in  maintaining  a  barometric 
column  of  mercury  at  the  height  of  760  millimetres 
is  called  one  atmosphere.)  Under  these  conditions 
hydrogen  became  visible  as  a  steel-blue  liquid,  a 
portion  of  which  solidified  as  it  issued  from  the  ap- 
paratus, and  fell  to  the  ground  in  grains.  These 
emitted  a  shrill,  metallic  sound  as  they  struck  the 
floor,  thus  emphasizing  the  idea  that  hydrogen  is 
really  a  metal.  Many  metals  can  be  converted  into 
gases  at  high  temperatures ;  mercury  becomes  gase- 
ous at  350°  centigrade,  and  is  liquid  under  ordinary 
circumstances.  The  gaseous  nature  of  hydrogen, 
therefore,  has  nothing  to  do  with  the  question 
whether  it  is  metallic  or  non-metallic.  The  chemi- 
cal significance  of  these  terms  will  appear  in  later 
chapters. 


CHAPTER  IV. 

OXYGEN. 

OXYGEN,  which  was  discovered  by  Priestley  in 
1774,  and  a  little  later,  but  independently,  by  Scheele, 
is  the  most  abundant  of  all  the  elements.  Uncom- 
bined,  but  mixed  with  nitrogen,  it  constitutes  one 
fifth  of  the  atmosphere ;  combined,  it  forms  eight 
ninths  of  the  material  composing  water,  and  about 
one  half  the  weight  of  all  the  rocks.  It  is  also  a 
very  important  constituent  of  animal  and  vegetable 
matter. 

Oxygen  was  originally  prepared  by  heating  mer- 
curic oxide  (see  Experiment  2),  mercury  being  left 
behind,  while  the  oxygen  was  given  off.  This  meth- 
od, however,  is  inconvenient,  and  is  now  replaced 
in  ordinary  practice  by  the  following  cheaper  pro- 
cess: 

EXPERIMENT  11.— Take  a  stout  test-tube,  or, 
better,  a  piece  of  glass  combustion-tubing  sealed  at 
one  end,  and  close  its  mouth  with  a  perforated  cork, 
through  which  is  inserted  a  delivery-tube,  also  of 
glass.  Mix  thoroughly  upon  a  sheet  of  paper  equal 
weights  of  potassium  chlorate  and  manganese  diox- 
ide, taking  care  that  both  are  perfectly  pure  and 
dry.  Fill  the  test-tube  one  third  full  with  this  mix- 
ture, and  heat  carefully  over  a  spirit-lamp  or  a 


OXYGEN.  25 

Bunsen  gas-burner.  Oxygen  will  be  given  off  co- 
piously, and  may  be  collected  either  in  a  rubber 
gas-bag,  or  in  several  bottles  over  water  in  the 
pneumatic  trough.  (Fig.  6.)  When  oxygen  is  to 
be  prepared  in  large  quantities,  a  copper  or  iron 
retort  is  used  instead  of  a  glass  tube.  For  safety, 
several  precautions  ought  to  be  observed.  First,  it 
is  well  to  heat  the  manganese  dioxide  to  redness  in 
an  iron  dish  before  using  it,  in  order  to  burn  out 


FIG.  6. — Preparation  of  Oxygen. 

any  deleterious  impurities.  Were  particles  of  or- 
ganic matter  or  charcoal  to  be  present,  a  dangerous 
explosion  might  ensue.  Secondly,  the  upper  por- 
tions of  the  mixture  in  the  tube  should  be  heated 
first,  and  later  the  lower  portions.  Thirdly,  the 
heat  should  be  so  regulated  that  the  oxygen  will  be 
given  off  in  a  steady,  tranquil  stream  ;  not  in  sudden 
gusts,  explosively. 

In  this  experiment  the  potassium  chlorate,  which 
consists  of  potassium,  chlorine,  and  oxygen  chemi- 


26  INORGANIC  CHEMISTRY. 

cally  combined,  is  decomposed  ;  the  oxygen  being 
set  free,  while  potassium  chloride,  a  compound  of 
potassium  and  chlorine,  remains  behind.  The  man- 
ganese dioxide  undergoes  no  change,  but  in  some 
way  it  facilitates  the  decomposition  of  the  chlorate. 
This  kind  of  action,  in  which  a  body  assists  a  chemi- 
cal process  without  being  itself  altered,  is  often  met 
with,  and  is  termed  catalytic  action.  Some  cases  of 
catalysis  are  easily  explained,  but  this  particular  case 
awaits  an  explanation.  Several  other  processes  for 
preparing  oxygen  are  somewhat  in  use,  and  one  or 
two  of  them  will  be  hereafter  referred  to. 

Oxygen  is  a  colorless,  tasteless,  odorless  gas,  six- 
teen times  heavier  than  hydrogen.  By  cooling  to 
a  temperature  of  —140°  centigrade,  under  a  press- 
ure of  320  atmospheres,  it  has  been  condensed  to  a 
colorless  liquid.  It  unites  with  all  the  other  ele- 
ments, except  fluorine,  and  its  compounds  with 
them  are  called  oxides.  For  example,  with  zinc  it 
forms  zinc  oxide ;  with  copper,  copper  oxide,  etc. 
Water,  in  chemical  nomenclature,  can  be  called 
hydrogen  oxide.  The  names  of  chemical  com- 
pounds are  intended  to  express,  more  or  less  per- 
fectly, their  composition.  When  oxygen  unites  with 
other  substances,  the  process  is  termed  oxidation. 

The  most  characteristic  property  of  oxygen  is  its 
power  of  sustaining  combustion.  In  nearly  all  cases 
combustion  is  merely  oxidation  accompanied  by  the 
development  of  heat  and  light.  When  oxygen  is  ex- 
cluded from  a  burning  body,  the  fire  goes  out.  In 
the  air,  we  have  one  fifth  of  oxygen  diluted  with 
four  fifths  of  nitrogen,  the  latter  element  being  inert 
and  exerting  no  direct  influence  upon  combustion 
whatever.  Naturally,  combustion  takes  place  much 


OXYGEN. 


more  vividly  in  pure  oxygen  than  in  diluted  oxygen 
(or  air),  as  the  following  easy  experiments  will  show : 

EXPERIMENT  12. —  Blow  out  a  lighted  candle, 
leaving  a  glowing  spark  at  the  end  of  the  wick. 
Lower  the  candle  into  a  bottle  or  jar  of  oxygen,  and 
the  wick  will  relight,  burning  far  more  brightly  than 
before. 

EXPERIMENT  13. — Charcoal  burns  in  the  air  with- 
out flame,  with  only  a  dull-red  glow.  Plunge  a  bit 
of  ignited  charcoal  into  a  jar  of  oxygen,  and  it  will 
burn  brilliantly. 

EXPERIMENT  14. — Kindle  a  bit  of  sulphur  in  a 
deflagrating  spoon,  and  note  the  insignificant  flame. 
Now  lower  it  into  pure  oxygen,  and  the  combus- 
tion will  become  exceedingly  vivid  (Fig.  7). 

EXPERIMENT  15.  — 
Repeat  the  last  experi- 
ment, using  a  much 
larger  jar  of  oxygen, 
and  burning  phosphor- 
us instead  of  sulphur. 
The  combustion  will  be 
so  dazzlingly  brilliant 
that  the  experiment  has 
sometimes  been  fanci- 
fully called  "the  phos- 
phoric sun." 

EXPERIMENT  16. — 
Some  substances  which 
do  not  ordinarily  burn 

in  air  burn  easily  in  pure  oxygen.  For  example, 
fasten  a  bit  of  steel  watch-spring  to  a  stout  wire,  and 
dip  the  end  of  it  in  melted  sulphur.  Kindle  the 
latter  and  immerse  the  spring  in  oxygen.  Present- 


Flo.  7. — Combustion  in  Oxygen. 


28  INORGANIC  CHEMISTRY. 

ly  the  steel  itself  will  ignite,  burning  brilliantly  and 
sending  forth  a  shower  of  sparks.  It  will  be  well 
to  cover  the  bottom  of  the  oxygen-jar  with  sand, 
to  catch  any  particles  of  melted  metal  which  may 
fall. 

Oxygen  is  also  essential  to  respiration.  Exclude 
it  from  the  lungs,  and  death  follows,  as  in  cases  of 
drowning,  when  the  lungs  become  filled  with  water. 
Inclose  a  small  animal  in  a  limited  volume  of  air, 
and  it  lives  only  until  the  supply  of  oxygen  con- 
tained in  it  is  exhausted.  In  pure  oxygen  it  will 
live  much  longer,  but  the  vital  processes  will  go 
on  too  violently  and  rapidly,  and  death  will  result.* 
Even  the  fishes  need  oxygen,  and  they  secure  it 
through  their  gills  from  the  air  which  is  dissolved 
in  the  water.  In  a  shallow  pool  insufficiently  sup- 
plied with  air  a  fish  will  soon  die. 

Oxygen  is  administered  by  physicians  to  a  cer- 
tain extent  as  a  remedy  in  cases  of  impeded  breath- 
ing. A  croupy  or  asthmatic  patient,  for  instance, 
can  not  get  enough  air  for  proper  respiration ;  but 
upon  breathing  a  little  pure  oxygen  he  will  experi- 
ence great  relief.  When  the  lungs  are  filled  with 
oxygen  instead  of  air,  it  is  possible  to  "  hold  the 
breath  "  much  longer  than  ordinarily — a  fact  which 
might  be  used  by  divers.  Oxygen  is  now  made  for 
sale  in  most  of  our  large  cities.  It  is  used  chiefly  in 
the  calcium-light  (see  next  chapter),  and  is  stored  up 
under  compression  in  strong  iron  cylinders. 

The  fact  that  oxygen  dissolves  somewhat  in  wa- 
ter, as  hinted  in  a  preceding  paragraph,  is  one  of 
vast  importance  in  the  economy  of  Nature.  In  the 

*  In  the  chapter  upon  carbon  the  phenomena  of  combustion  and 
respiration  will  be  treated  more  fully. 


OXYGEN. 


29 


falling  of  the  rain,  the  agitation  of  the  waves,  and  the 
flowing  of  streams,  water  is  being  constantly  charged 
with  fresh  supplies  of  air.  The  oxygen  thus  ab- 
sorbed at  once  attacks  the  decaying  animal  and 
vegetable  matter  which  is  continually  flowing  into 
rivers,  lakes,  and  oceans,  and  by  a  process  of  slow 
combustion  literally  burns  it  up.  Thus  oxygen  be- 
comes a  great  disinfectant,  transforming  noxious 
substances  into  simpler  and  harmless  compounds, 
and  keeping  the  waters  of  our  planet  always  sweet 
and  clean.  In  a  similar  way  it  oxidizes  injurious 
vapors  in  the  air,  and  is  effective  in  the  removal  of 
all  kinds  of  corruption  from  the  face  of  the  earth. 
All  decay  involves  the  phenomenon  of  oxidation. 

Many  elements,  and  possibly  all  of  them,  are  ca- 
pable of  existing  in  more  than  one  modification. 
For  example,  carbon  exists  as  charcoal,  as  graphite 
or  "  black-lead,"  and  as  diamond  ;  and  similar  prop- 
erties are  strikingly  displayed  by  phosphorus  and 
sulphur.  This  phenomenon  is  called  allotropy,  and 
charcoal,  grapm'te,  and  diamond  are  termed  allotropic 
modifications  of  carbon. 

When  an  electrical  machine  is  rapidly  worked, 
or  when  a  series  of  electrical  sparks  are  passed 
through  air,  a  peculiar  odor,  something  like  that 
of  burning  sulphur,  soon  becomes  noticeable.  This 
odor  is  due  to  the  formation  of  an  allotropic  modi- 
fication of  oxygen,  to  which  the  name  of  ozone  has 
been  given. 

EXPERIMENT  17.  —  Suspend  a  freshly-scraped 
stick  of  phosphorus  in  a  jar  containing  a  little  wa- 
ter, so  that  it  shall  be  partly  immersed.  It  will 
slowly  oxidize  ;  and  soon  the  air  in  the  jar  will  ac- 
quire the  peculiar  odor  of  ozone. 


30  INORGANIC  CHEMISTRY. 

Ozone  has  properties  quite  unlike  those  of  ordi- 
nary oxygen.  It  not  only  has  a  characteristic  suffo- 
cating odor,  but  it  exhibits  a  remarkable  chemical 
activity,  attacking  and  tarnishing  metals  like  silver 
and  mercury,  which  common  oxygen  does  not  affect 
at  all.  It  bleaches  many  vegetable  colors,  like  indi- 
go, deodorizes  putrefying  animal  matter,  and  cor- 
rodes such  substances  as  cork,  India-rubber,  etc.  A 
common  test  for  it  is  paper  soaked  in  a  solution  of 
potassium  iodide  and  starch.  Moist  slips  of  such 
paper,  exposed  to  the  action  of  ozone,  turn  blue  ; 
because  the  ozone  liberates  iodine  from  the  potas- 
sium iodide,  and  iodine  forms  a  blue  compound  with 
starch. 

In  ordinary  experiments  only  a  very  small  por- 
tion of  any  mass  of  oxygen  can  be  transformed  into 
ozone.  The  transformation  is,  however,  attended 
by  a  shrinkage  in  the  volume  of  the  oxygen,  so  that 
ozone  is  really  oxygen  in  a  more  concentrated  state. 
Three  volumes  of  oxygen  would  yield,  if  wholly 
converted  into  ozone,  only  two  volumes  of  the  lat- 
ter ;  whence  it  is  easy  to  see  that,  bulk  for  bulk, 
ozone  is  half  as  heavy  again  as  oxygen.  The  full 
significance  of  this  fact  will  appear  in  a  later  chap- 
ter. Quite  recently,  ozone  has  been  liquefied  by 
the  application  of  cold  and  pressure.  Liquid  ozone 
has  a  deep  indigo-blue  color,  and  is  less  volatile  than 
liquefied  oxygen. 

Ozone  is  continually  being  produced  in  nature, 
both  by  the  electric  discharges  which  take  place 
during  thunder-storms,  and  by  the  many  phenomena 
of  slow  oxidation  which  may  be  observed  in  the 
vegetable  kingdom.  It  undoubtedly  plays  an  im- 
portant part  in  the  world  as  a  natural  disinfectant, 


OXYGEN.  3I 

but  upon  this  point  much  remains  to  be  discovered. 
At  one  time  a  third  variety  of  oxygen,  named  anto- 
zone,  was  supposed  to  exist ;  but  the  evidence  in 
favor  of  it  is  now  generally  considered  unsatisfac- 
tory. 


CHAPTER  V. 

WATER. 

ALTHOUGH  oxygen  and  hydrogen  gases  may 
be  mixed  together  in  any  proportions,  they  unite 
chemically  to  form  only  two  real  compounds,  both 
of  which  at  ordinary  temperatures  are  liquids.  One 
contains  exactly  twice  as  much  oxygen  as  the  other, 
and  on  this  account  the  names  hydrogen  monoxide 
and  hydrogen  dioxide  are  respectively  applied  to 
them.  In  chemical  nomenclature  numeral  prefixes 
have  to  be  frequently  employed. 

When  oxygen  and  hydrogen  combine  directly, 
that  is,  without  the  intervention  of  other  substances, 
only  hydrogen  monoxide  or  water  is  produced. 
The  dioxide  is  prepared  by  indirect,  roundabout 
processes. 

The  formation  of  water  from  oxygen  and  hydro- 
gen may  be  brought  about  either  by  the  passage  of 
an  electric  spark  through  the  mixed  gases,  or  by 
the  agency  of  heat.  Whenever  hydrogen  or  any 
compound  of  hydrogen  is  burned,  water  is  pro- 
duced ;  as  was  partly  demonstrated  in  Experiment 
7.  All  ordinary  illuminating  materials,  such  as  coal- 
gas,  oils,  candles,  etc.,  contain  hydrogen ;  and  if  a 
piece  of  cold  porcelain  be  held  for  a  moment  over 
their  flames,  the  deposition  of  dew  will  show  that 
water  is  actually  formed. 


WATER.  33 

Under  ordinary  circumstances  the  combustion 
of  hydrogen  takes  place  quietly ;  but  if  it  be  burned 
in  pure  oxygen  some  extraordinary  phenomena  may 
be  observed. 

EXPERIMENT  18. — Fill  an  India-rubber  gas-bag 
with  a  mixture  of  two  parts  by  volume  of  hydrogen 
and  one  part  of  oxygen.  Then,  as  in  Experiment  9, 
attach  a  clay  pipe  to  the  bag  and  use  the  gaseous  mix- 
ture for  blowing  soap-bubbles.  Each  bubble,  when 
touched  with  a  lighted  candle,  will  explode  with  a 
violent  report.  If  a  heap  of  bubbles  be  blown  in  a 
common  tin  basin  and  ignited,  the  explosion  will  be 
deafening.  Before  applying  a  flame  to  any  of  the 
bubbles  the  stop-cock  of  the  bag  should  be  closed 
and  the  bag  itself  removed.  Serious  accidents 
have  happened  from  the  ignition  of  large  mixtures 
of  oxygen  and  hydrogen.  Even  coal-gas  and  com- 
mon air  will  give  a  powerfully  explosive  mixture, 
fully  as  dangerous  as  gunpowder.  This  is  shown 
by  the  terrible  explosions  which  sometimes  occur 
when  a  light  is  carelessly  carried  into  a  room  in 
which  gas  has  been  escaping. 

This  experiment  shows  us  that  the  formation  of 
water  from  its  elements  is  attended  by  a  remark- 
able development  of  force  or  energy.  This  force 
may  be  best  measured  in  the  form  of  heat :  and  it  is 
found  that  more  heat  is  produced  in  this  chemical 
change  than  in  any  other  chemical  change  what- 
ever. The  usual  unit  of  heat  is  the  quantity  of  heat 
needed  to  raise  the  temperature  of  one  gramme  of 
water  from  o°  to  i°  C. ;  and  in  the  combustion  of 
one  gramme  of  hydrogen  34,462  such  units  of  heat 
are  set  free.  A  gramme  of  charcoal,  burning,  yields 
only  8,080  heat-units — a  figure  in  striking  contrast 


34  INORGANIC  CHEMISTRY. 

with  the  foregoing.  When  hydrogen  burns  in  ordi- 
nary air,  just  as  much  heat  is  developed  as  if  the 
combustion  took  place  in  pure  oxygen ;  but  the 
temperature  of  the  flame  is  lower — partly  because 
the  heat  is  generated  more  slowly,  and  partly  be- 
cause much  of  it  is  expended  in  warming  the  ni- 
trogen with  which  the  oxygen  of  the  atmosphere 
is  diluted.  By  using  pure  oxygen  instead  of  air,  an 
enormously  high  temperature  may  be  attained  and 
utilized. 

Although  mixtures  of  oxygen  and  hydrogen  ex- 
plode violently  when  ignited,  the  two  gases  may  be 
made  to  burn  together  quietly  by  mingling  them 
just  at  the  moment  of  combustion.  This  is  done  in 
the  compound  (or  oxyhydrogen)  blow-pipe  invented 
by  Dr.  Hare.  In  this  apparatus  (Fig.  8)  the  oxygen 


FIG.  8. — Oxyhydrogen  Blow-pipe. 

and  hydrogen  are  contained  in  two  separate  bags 
or  cylinders.  They  are  mixed  just  at  the  tip  of 
the  burner  (Fig.  9),  which  consists  of  two  tubes, 
one  within  the  other.  Through  the  central  or  inner 
tube  oxygen  is  allowed  to  flow,  while  the  outer  tube 
connects  with  the  hydrogen-reservoir.  The  hydro- 
gen is  first  turned  on  and  kindled,  then  the  oxygen 


WA  TER. 


35 


is  admitted  ;  the  flow  of  both  gases  being  carefully 
regulated  by  stop-cocks,  and  by  pressure  on  the 
bags.  The  flame,  although  almost  non-luminous,  is 
intensely  hot;  and  many  substances  which  were 


FIG.  9. — Oxyhydrogen  Blow-pipe  Tip. 

once  deemed  infusible  melt  in  it  easily.  Platinum, 
for  example,  melts  like  wax  before  the  compound 
blow-pipe,  although  in  the  hottest  furnace  it  only 
softens.  In  the  metallurgy  of  platinum  this  fact 
is  carefully  utilized.  Some  metals,  like  silver,  are 
vaporized  by  the  heat  of  the  oxy hydrogen  jet, 
while  others  burn  in  it  brilliantly.  A  steel  file,  for 
instance,  is  easily  consumed,  sending  forth  a  mag- 
ficent  shower  of  sparks  as  it  burns. 

When  any  substance  capable  of  resisting  the 
excessively  high  temperature  is  inserted  in  the 
oxyhydrogen  flame,  it  becomes  intensely  luminous. 
This  fact  is  applied  in  the  calcium  or  Drummond 
light,  now  extensively  used  in  stereopticon  exhibi- 
tions and  for  theatrical  effects.  This  light  con- 
sists simply  of  a  small  cylinder  of  common  lime, 
upon  which  the  flame  of  a  compound  blow-pipe 
is  allowed  to  play.  It  rivals  the  electric  light  in  in- 
tensity. 

Up  to  this  point  we  have  been  considering  only 
the  qualitative  composition  of  water,  and  the  phe- 
nomena attending  its  formation.  We  now  need  to 
enter  upon  quantitative  discussions,  both  as  to  the 


36  INORGANIC  CHEMISTRY. 

volumes  and  the  weights  of  the  oxygen  and  hydro- 
gen which  unite. 

Whenever  a  current  of  electricity  is  passed 
through  a  liquid  capable  of  conducting  it,  that 
liquid,  if  compound,  will  be  decomposed.  This 
method  of  decomposition  is  known  as  electrolysis. 
Pure  water  is  not'  a  conductor  of  electricity,  but  by 
adding  to  it  a  few  drops  of  sulphuric  acid  it  be- 
comes one,  and  is  then  capable  of  electrolytic  analy- 
sis. 

EXPERIMENT  19. — Fill  and  invert  two  test-tubes 
in  a  vessel  of  water  slightly  acidulated  with  sulphu- 
ric acid.  Now  bring  under  their  mouths  the  two 
terminal  wires  of  a  small  galvanic  battery,  best  of  a 
couple  of  Grove,  Bunsen,  or  Daniell  cells  (Fig.  10). 


FIG.  10. — Electrolysis  of  Water. 

Bubbles  of  gas  will  slowly  form  (more  rapidly  with 
a  more  powerful  battery)  and  rise  into  the  test-tubes, 


WA  TER. 


37 


displacing  the  water  which  they  at  first  contained. 
Allow  this  action  to  continue  until  enough  gas  has 
accumulated  for  convenient  examination,  and  notice 
that  one  tube  contains  just  twice  as  much  as  the 
other.  By  applying  a  match  to  the  more  volumi- 
nous gas  it  may  be  identified  as  hydrogen  ;  while  by 
plunging  an  ignited  splinter  of  wood  into  the  con- 
tents of  the  other  tube  oxygen  may  at  once  be  recog- 
nized. By  analysis,  therefore,  water  yields  two  vol- 
umes of  hydrogen  to  one  of  oxygen.  In  this  experi- 
ment the  battery-wires,  as  far  as  they  dip  into  the 
acidulated  liquid,  should  terminate  in  slips  of  plati- 
num. 

The  foregoing  method  of  analysis  is  not  rigidly 
exact,  for  the  reason  that  traces  of  the  gases  evolved, 
and  rather  more  of  the  oxygen  than  of  the  hy- 
drogen, remain  dissolved  in  the  water.  Synthetic 
methods,  though  more  difficult,  are  better. 

When  an  electric  spark,  either  from  an  electri- 
cal machine,  a  Leyden-jar,  or  an  induction-coil,  is 
passed  through  a  mixture  of  hydrogen  and  oxygen, 
the  two  gases  unite  with  an  explosion.  For  quanti- 
tative purposes  this  experiment  is  usually  performed 
in  a  graduated  glass  tube,  called  a  eudiometer,  and 
the  spark  is  transmitted  between  two  platinum  wires 
which  are  melted  into  the  glass  at  the  closed  upper 
end  (Fig.  n).  In  such  a  tube  the  gases  can  be  ac- 
curately measured  ;  and  it  is  found  that  when  just 
two  volumes  of  hydrogen  and  one  of  oxygen  are 
taken,  the  union  is  complete.  If  the  mixture  of 
gases  contains  more  than  two  thirds  hydrogen  or 
more  than  one  third  oxygen,  the  excess  of  either 
element  simply  serves  to  dilute  the  rest,  and  re- 
mains unaltered  after  the  explosion.  The  oxygen 


38  INORGANIC  CHEMISTRY. 

and  hydrogen  under   these   circumstances   combine 
only  in  the  proportions  above  indicated.* 


FIG.  ii.  — Eudiometer. 

In  experiments  upon  the  union  of  gases  by  vol- 
ume an  important  question  always  arises — namely, 
Is  the  volume  of  the  product  the  same  as  that  of  the 
original  mixture,  or  does  condensation  occur  ?  Sup- 
pose, for  example,  that  two  litres  of  hydrogen  com- 
bine with  one  litre  of  oxygen,  and  that  we  measure 
the  volume  of  the  resulting  water  in  the  form  of 
steam.  We  shall  find  that,  if  we  compare  the  steam 
with  the  component  gases  at  identical  temperatures 
and  under  the  same  pressure,  only  two  litres  of 
steam  have  been  formed.  In  other  words,  the  three 
original  volumes  of  elementary  gases  have  con- 
densed to  two  volumes  during  union.  When  we 

*  For  class-room  illustration  this  experiment  may  be  roughly  per- 
formed with  improvised  apparatus,  as  far  as  demonstrating  the  effect 
of  an  electric  spark  is  concerned.  Accurate  work  is  hardly  possible 
under  such  circumstances. 


WATER, 


39 


come  to  consider  this  fact  in  its  relations  to  other 
facts  further  on,  we  shall  see  that  it  has  a  very 
important  bearing  upon  the  theories  of  chemistry. 
For  the  present  we  may  use  it  to  determine  the 
weight  of  steam  as  compared  with  that  of  hydro- 
gen. One  volume  of  oxygen  weighs  sixteen  times 
as  much  as  an  equal  volume  of  hydrogen.  Hence 
the  three  volumes  of  elementary  gases  which  unite 
to  form  water  must  weigh  i-)-i-f-i6r=  18  times  as 
much  as  one  volume  of  hydrogen.  But  this  is  also 
the  weight  of  two  volumes  of  steam,  so  that  one 
volume  of  steam  must  weigh  half  as  much,  and  be 
nine  times  heavier  than  hydrogen.  Furthermore, 
these  figures  give  us  the  composition  of  water  by 
weight.  The  one  volume  of  oxygen  must  be  just 
eight  times  as  heavy  as  the  two  volumes  of  hydro- 
gen, and  accordingly  water  consists  of  one  part  by 
weight  of  the  latter  element  to  eight  parts  of  the 
former.  This  ratio  of  one  to  eight  is  more  com- 
monly written  two  to  sixteen,  for  reasons  which  will 
appear  in  a  later  chapter. 

The  different  phenomena  and  substances  with 
which  chemistry  has  to  deal  are  so  intimately  con- 
nected one  with  another,  that  it  is  always  desirable 
to  verify  important  facts  by  several  distinct  lines  of 
investigation.  Since  the  composition  of  water  is  a 
matter  of  very  great  importance,  we  can  not  rest 
content  with  the  volumetric  analysis  and  synthesis 
given  above,  much  as  they  confirm  each  other,  but 
we  must  make  use  of  other  modes  of  demonstration 
also.  For  the  composition  of  water  by  weight  we 
have  so  far  only  an  indirect  estimation ;  and  for  ad- 
ditional proof  an  actual  synthesis  by  weight  must 
be  resorted  to.  This  is  best  accomplished  with  the 


40  INORGANIC  CHEMISTRY. 

aid  of  copper  oxide,  a  substance  containing  a  defi- 
nite quantity  of  oxygen  in  a  condition  very  available 
for  our  purposes. 

EXPERIMENT  20. — Place  a  quantity  of  dry  cop- 
per oxide  in  a  tube  of  hard  glass,  and  connect  the 
latter,  held  horizontally,  with  the  exit-tube  of  a  flask 
in  which  hydrogen  is  being  generated.  When  the 
apparatus  is  full  of  hydrogen,  so  that  an  explosion 


FIG.  12. — Synthesis  of  Water. 


due  to  admixed  air  may  be  no  longer  feared,  heat 
the  copper  oxide  carefully  to  near  redness  (Fig.  12). 
As  the  hydrogen  streams  over  it,  oxygen  will  be 
withdrawn  and  water  will  be  formed  ;  which,  as 
steam,  will  issue  from  the  farther  end  of  the  tube. 
When  the  operation  is  complete,  all  of  the  black  ox- 
ide will  have  been  reduced  to  pure,  bright,  metallic 
copper. 

This  experiment,  with  some  delicate  refinements, 


WATER.  4I 

gives  us  the  means  for  accurately  ascertaining  the 
weight-composition  of  water.  We  have  only  to 
weigh  the  copper  oxide  before  the  experiment,  and 
afterward  to  weigh  the  remaining  metallic  copper 
and  the  water  which  has  been  formed,  and  all  the 
necessary  data  are  at  our  disposal.  The  difference 
between  the  weights  of  the  copper  oxide  and  the 
copper  is  plainly  the  weight  of  the  oxygen  in  the 
water  produced.  This  weight,  subtracted  from  that 
of  the  water,  gives  us,  of  course,  the  weight  of  the 
hydrogen.  By  this  method,  water  is  found  to  con- 
tain, by  weight — 

88.89  per  cent  of  oxygen, 
1 1. 1 1         "        "  hydrogen. 


loo.oo  total. 

These  figures  give  us,  in  strict  accordance  with 
those  calculated  from  the  volumes  of  the  two  gases, 
the  ratio  of  one  to  eight,  or  two  to  sixteen,*  between 
the  weights  of  oxygen  and  hydrogen  in  water. 
Water,  then,  contains,  by  volume,  two  of  hydrogen 
to  one  of  oxygen,  these  three  volumes  being  con- 
densed by  union  into  two.  By  weight  it  contains 
two  parts  of  hydrogen  and  sixteen  of  oxygen — fig- 
ures which  we  shall  have  occasion  to  use  repeatedly 
hereafter. 

Water,  or  hydrogen  monoxide,  is  a  transparent, 
tasteless,  odorless  liquid.  In  small  quantities  it  ap- 
pears colorless  also,  but  in  thick  layers  it  is  found 
to  have  a  decided  blue  tint.  Its  physical  properties 
are  of  the  highest  importance,  inasmuch  as  they 

*  The  ratio  actually  deduced  from  all  the  best  experiments  is 
2  :  15.9633.  The  latter  figure  is  so  nearly  16  that  16  may  fairly  be 
used  in  ordinary  calculations. 


42  INORGANIC  CHEMISTRY. 

furnish  some  of  the  most  convenient  standards  with 
which  to  compare  those  of  other  substances.  Our 
thermometric  scales,  for  example,  depend  upon  the 
boiling  of  water  and  the  melting  of  ice ;  the  boiling- 
point  being  taken  as  one  standard  of  temperature 
and  the  melting-point  as  another.  In  the  centi- 
grade scale,  which  alone  is  used  in  this  book,  the 
temperature  at  which  ice  melts  or  water  freezes  is 
arbitrarily  put  at  zero,  while  the  boiling-point  is 
given  the  value  of  100°.  The  interval  between  is 
divided  into  one  hundred  equal  parts,  and  similar 
degrees  are  marked  off  for  temperatures  above  or 
below  the  two  standards.  The  Fahrenheit  scale, 
which  is  the  one  in  common  use,  assumes  32°  for 
the  freezing-point  of  water  and  212°  for  the  boiling- 
point,  dividing  the  space  between  into  one  hundred 
and  eighty  degrees. 

When  boiled,  water  yields  a  larger  volume  of 
vapor  than  any  other  known  liquid.  One  litre  of 
water,  measured  at  o°  C.,  converted  into  steam 
at  100°,  will  give  1,696  litres  of  the  latter.  Hence 
the  common  expression  that  "  a  cubic  inch  of  water 
yields  a  cubic  foot  of  steam  "  is  approximately  true. 
But  few  other  liquids  out  of  the  hundreds  known 
give  even  one  third  as  great  a  volume  of  vapor. 

Upon  cooling,  water  again  behaves  remarkably. 
It  contracts  regularly  until  the  temperature  of  4°  is 
reached,  at  which  degree  it  attains  its  maximum 
density.  Cooled  still  further,  it  expands,  and  at  o° 
it  solidifies  into  ice,  undergoing  another  more  sud- 
den expansion.  It  is  this  expansive  force  which 
breaks  bottles  and  pitchers  in  which  water  is  al- 
lowed to  freeze,  and  which  gives  to  frost  its  great 
power  in  disintegrating  rocks.  Because  of  the  ex- 


WATER. 


43 


pansion,  ice  is  lighter  than  water  and  floats  upon  it ; 
were  it  to  sink,  fresh  surfaces  of  liquid  would  be  ex- 
posed to  freezing  during  winter,  until  our  lakes  and 
rivers  were  frozen  solid.  Such  masses  of  ice  could 
not  be  melted  by  the  summer's  heat,  fish-life  would 
become  impossible,  and  the  temperate  zones  would 
in  time  be  almost  frigid.  When  the  vapor  of  wa- 
ter is  suddenly  chilled,  snow  is  formed,  and  every 
flake  exhibits  a  regular  crystalline  structure.  Each 


FIG.  13. — Snowflake  Crystals. 

snow-crystal  is  a  symmetrical,  six-pointed  star,  one 
varying  from  another  only  in  minor  particulars 
(Fig.  13).  Form  is  as  distinct  a  property  of  sub- 
stances as  color,  taste,  or  smell ;  and  every  solid 
has  its  own  characteristic  shape,  in  which,  if  left  to 
themselves,  its  molecules  become  arranged  in  ac- 
cordance with  rigid  mathematical  laws. 


44  INORGANIC  CHEMISTRY. 

As  regards  weight,  water  is  again  an  important 
standard.  In  the  metric  system  the  unit  of  weight 
is  the  gramme ;  and  this  is  denned  as  the  weight  of 
a  cubic  centimetre  of  water  measured  at  its  tem- 
perature of  maximum  density.  A  cubic  decimetre 
of  water,  or  a  litre,  weighs  just  a  thousand  grammes, 
or  one  kilogramme.  The  most  exact  weights  and 
measures,  therefore,  depend  for  their  accuracy  upon 
a  precise  knowledge  of  some  of  the  properties  of 
water. 

In  dealing  with  solids  and  liquids,  specific  grav- 
ity or  density  is  always  referred  to  water  as  the  unit 
of  comparison.  If  a  body  is  twice  as  heavy  as  water, 
bulk  for  bulk,  its  specific  gravity  is  said  to  be  two  ; 
if  five  times  heavier,  it  is  expressed  by  five,  and  so 
on.  The  specific  gravity  of  a  gas  or  vapor  is  now 
generally  referred  to  hydrogen  as  unity,  although 
in  some  works  air  is  still  retained  as  the  standard.* 

As  a  solvent,  water  far  exceeds  every  other  liquid 
known.  Certain  liquids,  like  alcohol  or  chloroform, 
will  dissolve  some  substances  which  water  can  not 
attack,  but  in  the  long  run  water  leads  them  all. 
As  a  general  rule,  with  comparatively  few  excep- 
tions, solids  dissolve  more  easily  in  hot  water  than 
in  cold.  Gases,  on  the  other  hand,  are  more  solu- 
ble in  cold  water.  Some  substances,  like  sugar,  dis- 
solve easily  and  in  large  quantity  in  water ;  others, 
as  for  example  gypsum,  dissolve  but  sparingly  ;  but 
for  each  one  there  is  a  limit  beyond  which  solu- 
bility can  not  go.  These  facts  may  advantageously 

*  Some  of  this  material  belongs  more  properly  in  a  work  on  physics, 
so  that  fuller  discussion  is  impracticable  here.  Such  physical  data  as 
have  chemical  importance  will  be  introduced  here  and  there  through- 
out this  volume. 


IV A  TER. 


45 


be  verified  by  the  student  with  self-devised  experi- 
ments upon  salt,  sugar,  alum,  and  such  other  soluble 
bodies  as  may  happen  to  be  most  readily  available. 
The  phenomenon  of  solution  is  one  which  has  not 
yet  been  fully  explained  ;  it  is  probably  due  to  a  very 
weak  kind  of  chemical  attraction  between  the  solv- 
ent liquid  and  the  substance  dissolved. 

Because  of  its  great  solvent  properties,  natural 
water  is  never  strictly  pure.  Rain-water  contains 
gaseous  impurities,  and  even  traces  of  solid  matter 
dissolved  in  it ;  while  river,  spring,  well,  and  lake 
waters  absorb  a  variety  of  substances  from  the  soil. 
Evaporate  any  ordinary  drinking-water  to  dryness 
on  a  slip  of  clean,  bright  platinum-foil,  and  you  will 
obtain  visible  traces  of  a  solid  residue.  In  sea-water, 
salt  lakes,  and  mineral  springs,  saline  substances  are 
present  in  large  quantities.  Effervescent  waters, 
like  those  of  the  Saratoga  springs,  are  also  heavily 
charged  with  a  well-known  gas,  carbon  dioxide  or 
carbonic  acid.  Waters  nearly  free  from  solid  ingre- 
dients are  called  soft  waters.  Waters  containing 
much  lime  in  solution  are  called  hard.  Perfectly 
pure  water  is  so  tasteless  as  to  seem  flat  and  un- 
drinkable.  Only  after  it  has  been  aerated  by  expos- 
ure to  the  air  does  it  become  palatable. 

Water  may  be  readily  freed  from  suspended 
sediments  either  by  settling  in  large  tanks  or  by  fil- 
tration. On  the  large  scale  it  is  best  filtered  by 
allowing  it  to  percolate  through  layers  of  charcoal 
and  sand,  but  in  the  laboratory  filters  of  paper  are 
commonly  used.  A  circular  sheet  of  unsized  paper 
is  doubled,  and  then  folded  again  at  right  angles  to 
the  crease  first  made.  By  lifting  one  of  the  folds 
away  from  the  other  three,  a  hollow  cone  of  paper 


46 


INORGANIC  CHEMISTRY. 


is  obtained  which  will  fit  snugly  to  the  sides  of  a 
glass  funnel.  When  water  containing  sediment  is 
poured  through  this  arrangement,  the  suspended 
solids  are  retained  by  the  paper,  and  the  liquid  is 
transmitted  clear  (Fig.  14). 

In  order  to  obtain  water  free  from  dissolved  im- 
purities, resort  must  be  had  to  distillation.     This 


FIG.  14.— Filtration. 

process  consists  simply  in  boiling  the  water  away, 
and  then  condensing  and  collecting  it  from  the 
steam.  Distillatory  apparatus  may  be  made  after  a 
great  variety  of  patterns,  according  to  the  exact  use 


WATER. 


47 


to  which  it  is  to  be  applied.     For  school  purposes, 
a  glass  retort  will  suffice,  arranged  as  shown  in  Fig. 


FIG.  15.— Distillation. 

15.  The  retort,  mounted  on  a  convenient  stand,  is 
half  filled  with  water  and  heated  by  a  lamp  placed 
below.  To  diminish  the  danger  of  breaking,  the 
bottom  of  the  retort  should  be  separated  from  the 
direct  flame  by  a  sheet  of  fine  wire-gauze.  ^  The  neck 
of  the  retort  dips  into  a  flask  called  a  receiver,  which, 
together  with  the  neck,  is  kept  cold  by  the  applica- 
tion of  wet  cloths.  When  the  water  in  the  retort  is 
boiled,  the  steam  passes  over  to  be  condensed  in  the 
receiver.*  From  gaseous  impurities  water  may  be 
freed  by  simple  boiling. 

Water  is  capable  of  entering  into  chemical  union 
with  many  other  substances.  A  great  number  of 
crystalline  salts  contain  definite  quantities  of  it,  in  a 

*  The  author  purposely  describes  the  apparatus  in  its  very  simplest 
form.  Schools  having  more  elaborate  appliances  will  of  course  use 
them. 


48  INORGANIC  CHEMISTRY. 

condition  known  as  water  of  crystallization.  Heat  a 
crystal  of  alum  in  a  glass  tube,  and  it  will  give  off 
water,  which  may  be  recognized  by  its  condensing 
in  drops  on  the  cooler  parts  of  the  tube  above.  Sul- 
phate of  copper  (blue  vitriol)  owes  its  brilliant  blue 
color  to  water  of  crystallization.  Upon  carefully 
heating  one  of  the  blue  crystals  it  will  become  white ; 
and  after  standing  a  while  it  will  regain  its  color  by 
absorption  of  water  from  the  atmosphere.  Many 
substances  have  this  power  of  absorbing  water  from 
the  air.  A  bit  of  calcium  chloride,  left  in  an  open 
vessel  for  a  few  days,  will  become  wet,  and  in  time 
will  even  liquefy,  so  much  water  is  taken  up.  This 
phenomenon  is  called  deliquescence.  When  a  body 
loses  water  spontaneously  it  is  said  to  effloresce. 
Many  minerals  contain  water  of  crystallization,  and 
water  is  an  essential  and  important  constituent  of 
all  animals  and  vegetables. 

The  second  compound  of  hydrogen  and  oxygen, 
hydrogen  dioxide,*  is  a  very  interesting  substance, 
but  hardly  important  enough  for  extended  descrip- 
tion here.  It  is  a  liquid  nearly  half  as  heavy  again 
as  water,  and  it  actively  bleaches  vegetable  colors. 
As  a  powerful  oxidizer  it  behaves  very  much  like 
ozone. 

*  Sometimes  called  peroxide  of  hydrogen. 


CHAPTER  VI. 

NITROGEN  AND   THE  ATMOSPHERE. 

NITROGEN,  which  was  discovered  by  Rutherford 
in  1772,  occurs  abundantly  in  the  atmosphere,  and 
also  as  an  important  constituent  of  animal  and  vege- 
table matter.  It  is  furthermore  contained  in  very 
many  artificial  substances  ;  as,  for  example,  nitric 
acid,  ammonia,  saltpeter,  nitroglycerine,  and  so  on. 
In  the  air  it  is  found  to  be  mixed  with  oxygen ;  and  it 
is  most  readily  isolated  by  simply  withdrawing  the 
latter  element  from  it. 

EXPERIMENT  21. —  Place  a  bit  of  carefully  dried 
phosphorus,  as  big  as  a  pea,  upon  a  piece  of  flat 
cork,  and  float  it  in  a  large  earthen  dish  half  full 
of  water.  Kindle  the  phosphorus,  and  then  cover 
it  with  a  capacious  glass  jar  or  bell-glass,  whichever 
happens  to  be  most  convenient  (Fig.  16).  In  burn- 
ing, the  phosphorus  is  of  course  only  uniting  with 
the  oxygen  of  the  air ;  and  white  clouds  of  a  solid 
oxide  of  phosphorus  are  formed.  These  dissolve 
in  the  water  of  the  dish,  and  at  last  the  gas  remain- 
ing in  the  jar  will  be  approximately  pure  nitrogen. 
This  may  be  allowed  to  stand  for  further  examina- 
tion. In  order  to  protect  the  cork  from  burning 
with  the  phosphorus,  the  latter  may  rest  directly 
upon  a  layer  of  either  plaster-of-paris  or  lime,  which 
will  serve  as  a  non-conductor  of  heat. 


INORGANIC  CHEMISTRY. 


Nitrogen  may  also  be  prepared  by  a  sort  of  re- 
versal of  Experiment  20.  In  that  experiment,  cop- 
per oxide  was  heated  in 
a  stream  of  hydrogen  ; 
water  being  formed, 
and  metallic  copper  re- 
maining behind.  Now, 
by  heating  the  copper 
to  redness  and  pass- 
ing over  it  a  slow  but 
steady  current  of  air, 
copper  oxide  will  be 

FIG.  i6.-Prqparatiohof Nitrogen,  reproduced,  and  only 

nitrogen  will  issue  from 

the  farther  end  of  the  tube.  There,  by  means  of  a 
delivery-tube,  made  to  dip  under  water,  it  may  be 
collected  in  jars  and  further  investigated.  There 
are  several  other  processes  for  the  preparation  of 
nitrogen,  but  they  need  no  description  here.* 

In  the  free  state  nitrogen  is  one  of  the  least  inter- 
esting of  the  elements.  It  is  a  colorless  gas,  four- 
teen times  heavier  than  hydrogen,  and  having  nei- 
ther taste  nor  odor.  It  is  incapable  of  supporting 
either  life  or  combustion  :  a  lighted  candle  plunged 
in  it  is  extinguished  ;  an  animal  immersed  in  it 
immediately  dies.  Its  occurrence  in  the  air,  how- 
ever, shows  that  it  is  not  poisonous ;  it  kills,  not 
by  any  deleterious  action,  but  simply  because  it 
lacks  the  power  of  keeping  up  the  vital  processes ; 
when  it  fills  the  lungs,  the  necessary  oxygen  is  ex- 
cluded. 

Nitrogen  combines  directly  with  only  a  very  few 

*  In  short  courses  of  study  the  experimental  preparation  of  nitrogen 
may  be  omitted  altogether. 


NITROGEN  AND    THE  ATMOSPHERE.          51 

of  the  other  elements,  such  as  boron,  silicon,  and  the 
rare  metals  titanium  and  tungsten.  Its  important 
compounds  with  oxygen,  hydrogen,  and  so  on,  are 
all  formed  by  indirect  processes,  and,  as  a  general 
rule,  are  very  easily  decomposed.  Nearly  all  of 
the  explosive  substances  practically  in  use  are  com- 
pounds of  nitrogen,  and  their  explosiveness  is  a 
consequence  of  this  ready  decomposibility.  Gun- 
powder, gun-cotton,  nitroglycerine,  dynamite,  and 
fulminating  powder,  are  all  cases  in  point. 

The  composition  of  air,  which  may  be  approxi- 
mately put  at  one  fifth  oxygen  with  four  fifths  nitro- 
gen, is  more  precisely  given  in  the  following  per- 
centages : 


By  weight. 

By  volume. 

Oxvsrcn   . 

2^.0 

20.8 

Nitrogen  

77.O 

70-2 

100.0 

1  00.0 

In  a  rough  way  the  composition  by  volume  may 
be  verified  in  a  class-experiment,  as  follows : 

EXPERIMENT  22.— Invert  a  large  test-tube,  or, 
better,  a  graduated  tube  closed  at  one  end,  in  a 
dish  containing  mercury  (Fig.  17).  Now  melt  under 
warm  water  a  little  phosphorus,  and  take  up  a  drop 
of  it  upon  the  end  of  a  stout  wire.  When  it  solidi- 
fies, pass  the  small  pellet  thus  formed  under  the  sur- 
face of  the  mercury  and  up  into  the  tube.  Leave  it 
in  position  for  several  hours,  or  longer  if  need  be. 
The  phosphorus  will  slowly  oxidize,  and  the  mer- 
cury will  gradually  rise  in  the  tube  until  but  four 
fifths  of  the  original  air  remains.  A  lighted  match 


52  INORGANIC  CHEMISTRY. 

plunged  into  this  remaining  gas  will  be  extinguished, 
showing  it  to  be  nitrogen. 


FIG.  17. — Analysis  of  Air. 

Air  is  only  a  mixture — not  a  chemical  compound. 
This  will  appear  more  clearly  after  we  study  the 
true  oxides  of  nitrogen  in  the  next  chapter.  Still, 


NITROGEN  AND    THE  ATMOSPHERE. 


53 


some  considerations  bearing  upon  this  point  may 
well  be  offered  here.  If  we  artificially  mix  oxygen 
and  nitrogen  gases  in  the  proper  proportions,  the 
mixture  will  have  all  the  characteristic  properties 
of  air,  and  yet  none  of  the  usual  phenomena  which 
attend  chemical  union  will  be  manifest.  Further- 
more, although  air  is  practically  constant  in  its 
composition,  whether  taken  from  the  tops  of  mount- 
ains or  the  depths  of  valleys,  from  near  the  Equator 
or  in  the  Arctic  zone,  it  does  exhibit  slight  varia- 
tions which  can  be  detected  by  refined  analyses. 
Some  remarkable  experiments  by  Professor  Morley 
illustrate  this  fact.  It  has  been  supposed  by  some 
meteorologists  that  the  sudden  periods  of  severe 
weather  popularly  known  as  "  cold  snaps  "  are  due 
to  the  vertical  descent  of  intensely  cold  air  from 
very  great  elevations.  Now,  oxygen  is  heavier  than 
nitrogen  in  the  ratio  of  sixteen  to  fourteen,  and  is 
consequently  more  powerfully  affected  by  gravita- 
tion. There  is,  therefore,  in  spite  of  the  ease  with 
which  gases  diffuse  into  each  other,  becoming  more 
and  more  perfectly  mixed,  a  slight  tendency  to  a 
concentration  of  the  heavier  oxygen  near  the  earth's 
surface,  and  a  corresponding  excess  of  nitrogen  at 
very  great  heights  above.  If,  now,  a  "  cold  snap  " 
is  caused  by  a  sudden  descent  of  air  from  an  exceed- 
ingly high  level,  the  air  during  it  should  be  slightly 
poorer  in  oxygen  than  at  other  times.  This,  by  a 
long  series  of  daily  analyses  of  air,  Professor  Mor- 
ley finds  to  be  the  fact ;  although  the  differences  are 
so  small  as  to  be  comparatively  unimportant. 

In  speaking  of  air  we  always  mean  the  gaseous 
mixture  above  described,  which  is  14.43  times  as 
heavy  as  hydrogen.  In  the  atmosphere  around  us, 


54  INORGANIC  CHEMISTRY. 

however,  several  other  substances  occur,  but  in 
widely  varying  proportions.  First,  the  vapor  of 
water  is  always  present,  and  plays  an  important 
part  in  determining  the  character  of  a  climate. 
Secondly,  carbon  dioxide  is  invariably  to  be  found, 
in  quantities  ranging  from  three  to  seven  volumes 
in  ten  thousand  volumes  of  air.  The  average 
amount  in  the  open  country  is  about  four  volumes ; 
at  sea  the  proportion  is  less,  and  near  large  towns 
it  is  greater.  Any  quantity  over  seven  volumes 
is  decidedly  injurious  to  health.  Small  as  these 
proportions  are,  the  total  quantity  of  carbon  dioxide 
in  the  atmosphere  is  enormous ;  and,  as  we  shall 
see  when  we  come  to  study  carbon,  its  influence  in 
connection  with  the  growth  of  plants  is  extremely 
important.  Thirdly,  ammonia  in  minute  traces  is  a 
regular  constituent  of  the  atmosphere.  This,  fre- 
quently combined  with  nitric  acid,  is  brought  down 
to  the  earth  by  snow  and  rain,  and  serves  to  supply 
plants  with  a  considerable  part  of  their  nitrogen. 
All  of  these  ingredients  of  the  atmosphere,  and 
probably  also  ozone,  are  essential,  and  necessary  in 
the  economy  of  nature.  With  them  various  acci- 
dental impurities  are  frequently  found,  products  of 
putrefaction,  of  combustion,  and  so  on. 


CHAPTER  VII. 

AMMONIA  AND  THE   OXIDES   OF  NITROGEN. 

THE  compounds  formed  by  the  union  of  nitro- 
gen with  hydrogen  and  oxygen  are  extremely  im- 
portant and  interesting,  both  from  a  practical  and 
from  a  theoretical  point  of  view. 

With  hydrogen  alone,  nitrogen  combines  in  only 
a  single  proportion ;  the  compound  being  the  well- 
known  substance,  ammonia.  We  have  already  seen 
that  this  body  occurs  in  minute  quantities  in  the 
atmosphere ;  it  is  also  found  in  rain  and  river  wa- 
ters, and  in  all  fertile  soils.  It  is  continually  pro- 
duced in  nature  by  the  decomposition  of  animal 
matter,  and  it  may  be  prepared  artificially  by  dis- 
tilling refuse  scraps  of  horn,  hoofs,  bones,  or  hair. 
In  the  manufacture  of  illuminating-gas  it  is  devel- 
oped from  the  nitrogen  contained  in  the  coal,  and  it 
is  retained  by  the  water  through  which  the  gas  is 
passed  on  its  way  to  the  gas-holders.  The  ammo- 
niacal  solution  thus  obtained  is  now  the  chief  com- 
mercial source  of  ammonia.  It  is  first  mixed  with 
sulphuric  acid,  forming  a  substance  known  as  am- 
monium sulphate,  which  is  used  to  some  extent 
as  a  fertilizer.  This  compound,  heated  with  lime, 
evolves  ammonia  copiously. 

EXPERIMENT  23. — Rub  together  in  a  mortar  a 


56  INORGANIC  CHEMISTRY. 

fragment  of  "  sal  ammoniac  "  (ammonium  chloride), 
a  bit  of  lime,  and  a  few  drops  of  water.  Ammonia 
will  be  set  free  and  may  be  recognized  by  its  smell. 
All  compounds  of  ammonia  behave  in  the  same 
way  ;  so  that  trituration  with  lime  affords  a  ready 
means  of  testing  for  the  substance. 

EXPERIMENT  24. — Pulverize  two  parts  by  weight 
of  ammonium  chloride  and  one  part  of  quicklime. 
Mix,  and  transfer  the  mixture  to  a  stout  glass  flask 
provided  with  a  delivery-tube  (Fig.  18).  Upon 
heating,  ammonia  will  be  freely  given  off,  and  it 


FIG.  18. — Preparation  of  Ammonia. 

can  be  collected  in  test-tubes  or  small  bottles  in- 
verted over  mercury.  The  usual  pneumatic  trough 
or  water-pan  can  not  be  used  in  this  case,  because 
of  the  solubility  of  ammonia  in  water. 

Ammonia,  thus  prepared,  is  a  colorless  gas  of  a 
peculiar,  characteristic,  very  pungent  odor.  Under 
ordinary  circumstances  it  is  neither  combustible  nor 


AMMONIA  AND  THE  OXIDES  OF  NITROGEN.   57 

a  supporter  of  combustion ;  but,  mixed  with  a  large 
quantity  of  oxygen,  it  may  be  made  to  burn  with  a 
yellow  flame.  By  weight  it  is  composed  of  four- 
teen parts  of  nitrogen  united  with  three  of  hydro- 
gen ;  or,  by  bulk,  one  volume  of  the  former  gas  to 
three  of  the  latter.  These  four  volumes  condense 
to  two  in  the  compound,  the  ammonia  formed  being 
eight  and  one  half  times  heavier  than  hydrogen. 
These  figures  carry  weighty  significance,  which  will 
appear  in  the  next  chapter. 

Ammonia  is  extremely  soluble  in  water,  particu- 
larly when  the  latter  is  cold.  At  the  temperature 
of  o°  Q,  one  cubic  centimetre  of  water  will  absorb 
1,148  c.  c.  of  the  gas  ;  while  at  15°  only  783  c.  c.  will 
be  taken  up.  This  solubility  may  be  illustrated  by 
introducing  a  few  drops  of  water  into  one  of  the 
tubes  filled  with  ammonia  during  Experiment  24, 
and  left  in  position  over  mercury.  The  water  will 
absorb  the  gas  almost  instantaneously,  and  the  mer- 
cury will  suddenly  rise  to  take  its  place  in  the  tube. 

The  aqueous  solution  of  ammonia  is  the  common 
aqua  ammonia,  ammonia-water,  or  spirits  of  harts- 
horn of  the  shops.  The  last  name  reminds  us  that 
ammonia  was  at  one  time  prepared  from  the  horns 
of  deer.  Ammonia-water  is  used  to  some  extent  in 
medicine,  and  has  many  important  applications  in 
chemical  manufactures.  It  varies  much  in  strength, 
but  it  always  has  the  characteristic  odor  of  the 
gas,  and  is  strongly  alkaline.  It.  is  also  caustic; 
and,  when  strong,  readily  blisters  the  skin.  When 
boiled,  it  gives  off  its  gaseous  ammonia.  The  latter, 
by  cold  and  great  pressure,  is  easily  condensed  to  a 
colorless  liquid,  which,  when  the  pressure  is  re- 
leased, rapidly  evaporates,  producing  intense  cold. 


58  INORGANIC  CHEMISTRY. 

This  fact  is  applied  in  Carre's  machine  for  making 
artificial  ice.*  All  ice-machines  depend  upon  the 
principle  that  a  liquid,  in  evaporating,  absorbs  heat 
from  surrounding  objects.  Liquefied  gases  evapo- 
rate suddenly,  and  therefore  absorb  heat  suddenly. 

With  oxygen,  nitrogen  unites  in  five  different 
proportions ;  and  two  of  its  oxides  combine  further 
with  water  to  form  two  well-known  acids.  Since 
nitric  acid  is  the  most  convenient  starting-point  for 
the  preparation  of  all  these  other  compounds,  it 
may  properly  be  the  next  substance  to  engage  our 
attention. 

EXPERIMENT  25. — Arrange  a  retort  and  receiver 
as  in  Fig.  15.  Put  a  weighed  quantity  of  saltpeter 
(potassium  nitrate)  in  the  retort,  pour  over  it  an 
equal  weight  of  strong  sulphuric  acid,  and  heat. 
Nitric  acid  will  distil  over ;  and  at  last  a  white  solid, 
'potassium  hydrogen  sulphate,  will  remain  behind. 

In  the  commercial  manufacture  of  nitric  acid 
sodium  nitrate  is  used  instead  of  saltpeter,  being 
cheaper.  But  any  nitrate,  distilled  with  sulphuric 
acid,  will  yield  nitric  acid  in  the  same  way.  -  Ni- 
trates are  simply  the  compounds  formed  by  nitric 
acid  with  the  various  metals  and  bases,  and  all  have 
names  similar  to  those  mentioned  above.  Sulphu- 
ric acid  is  stronger  than  nitric  acid,  and  displaces 
it  from  its  compounds,  forming  sulphates  instead. 
Such  names  as  silver  nitrate,  lead  nitrate,  copper 
sulphate,  and  zinc  sulphate,  are  good  examples  of 
this  kind  of  nomenclature.  Similarly,  carbonic  acid 
forms  carbonates ;  boric  acid,  borates ;  phosphoric 
acid,  phosphates ;  acetic  acid,  acetates,  and  so  on. 

*  See  "  Roscoe  and  Schorlemmer's  Chemistry,"  vol.  i,  p.  3^3  I  or 
"  Deschanel's  Physics,"  pp.  329-330. 


AMMONIA  AND  THE  OXIDES  OF  NITROGEN.   59 

Nitric  acid,  when  pure,  is  a  colorless  liquid  of 
specific  gravity  1.52.  Commonly  it  is  somewhat 
yellow,  from  the  presence,  as  an  impurity,  of  one 
of  the  oxides  of  nitrogen.  It  has  a  suffocating  odor, 
an  intensely  sour  taste,  and  is  exceedingly  corrosive. 
It  attacks  all  ordinary  metals  except  gold  and  plat- 
inum ;  and,  indeed,  dissolves  most  of  them.  Hence 
the  early  chemists  gave  it  the  name  of  aquafortis,  or 
"  strong  water."  Applied  to  the  skin,  it  produces 
yellow  stains,  which  wear  off  only  after  several 
days ;  and,  if  strong,  it  causes  corrosion  as  painful 
as  a  burn.  Physicians  use  it  somewhat  as  a  caustic ; 
it  is  employed  in  etching  copper  plates  for  engrav- 
ings; and  it  has  important  applications  in  refining 
the  precious  metals,  in  making  nitroglycerine,  gun- 
cotton,  the  aniline  dyes,  and  so  on.  The  following 
experiments  with  nitric  acid  will  be  found  instruc- 
tive: 

EXPERIMENT  26. — Cover  a  piece  of  bright  sheet 
copper  with  a  thin  coating  of  wax.  Scratch  a  de- 
sign through  the  wax  with  a  sharp  needle.  Now 
pour  over  the  sheet  a  little  nitric  acid,  previously 
diluted  with  an  equal  bulk  of  water,  and  after  a  few 
minutes  wash  it  off  again.  Upon  cleaning  off  the 
wax  the  design  will  be  found  to  be  etched  into  the 
copper. 

EXPERIMENT  27. — Cover  a  bit  of  lead  in  a  glass 
or  porcelain  dish  with  nitric  acid  diluted  as  before. 
Reddish  fumes  will  be  given  off,  and  the  metal  will 
dissolve.  If  the  solution  be  allowed  to  stand  for  a 
while,  or  if  it  be  boiled  down  somewhat,  it  will  de- 
posit white  crystals  of  lead  nitrate.*  These  can  be 

*  This  experiment  may  be  varied  by  using  other  metals  than  lead 
and  getting  other  nitrates.     Any  common  metal  will  do,  except  tin  or 


60  INORGANIC  CHEMISTRY. 

used,  if  time  permits,  in  a  repetition  of  Experiment 
25  for  the  preparation  of  nitric  acid. 

EXPERIMENT  28. — Pour  dilute  nitric  acid  over  a 
few  clippings  of  quill,  bits  of  white  feather,  or  fibres 
of  white  silk.  They  will  be  stained  permanently 
yellow. 

EXPERIMENT  29. — Put  a  fragment  of  any  nitrate 
into  a  test-tube,  and  dissolve  it  in  the  smallest  pos- 
sible quantity  of  water.  Add  to  the  solution,  cau- 
tiously, an  equal  bulk  of  strong  sulphuric  acid,  and 
allow  the  mixture,  which  has  become  hot,  to  cool. 
In  another  test-tube  dissolve  with  water  a  crystal  of 
sulphate  of  iron.  Pour  this  solution,  very  slowly, 
into  the  first  test-tube,  holding  the  latter  slantwise, 
so  that  the  two  fluids  will  form  two  separate  layers, 
without  mixing.  At  the  boundary  between  these 
layers  a  brown  ring  will  appear.  This  is  the  test 
by  means  of  which  nitric  acid  and  nitrates  are  ordi- 
narily detected. 

In  speaking  of  ammonia  it  was  described  as  be- 
ing strongly  alkaline.  Inasmuch  as  the  terms  acid 
and  alkaline  will  be  frequently  used  in  this  book,  the 
distinction  between  them  may  well  be  illustrated 
here. 

EXPERIMENT  30. — Into  one  test-tube  of  water 
pour  a  few  drops  of  nitric  acid,  and  into  another  a 
little  ammonia.  Into  the  one  containing  the  acid 
dip  a  slip  of  blue  litmus-paper.*  It  will  become 
red ;  and  if  it  be  now  inserted  into  the  ammonia  the 

antimony.  These,  instead  of  dissolving,  are  converted  into  white,  in- 
soluble oxides. 

*  Litmus  is  a  coloring  matter  obtained  from  certain  lichens.  The 
juice  of  the  common  red  cabbage  may  be  used  as  a  substitute  for  it ; 
being  turned  green  by  alkalies  and  regaining  its  tint  with  acids. 


AMMONIA  AND  THE  OXIDES  OF  NITROGEN.   6 1 

blue  color  will  be  restored.  Blue  litmus,  then,  is 
reddened  by  an  acid,  and  reddened  litmus  is  turned 
blue  by  an  alkali.  An  alkali  is  in  its  chemical  prop- 
erties the  opposite  of  an  acid  ;  and  in  litmus-paper 
we  have  a  convenient  means  of  recognizing  either 
class  of  substances. 

Any  substance  which  unites  with  an  acid  is 
termed  a  base.  The  compounds  formed  are  known 
as  salts,  and,  in  general,  have  no  effect  upon  litmus- 
paper.  Strictly  speaking,  the  alkalies  are  simply 
the  stronger  soluble  bases,  of  which  soda,  potash, 
and  ammonia*  are  the  best  examples.  Lime  is  also 
strongly  alkaline.* 

EXPERIMENT  31. — Put  a  slip  of  litmus-paper  in  a 
porcelain  or  glass  dish  containing  ammonia,  and  add 
nitric  acid  cautiously,  stirring  meanwhile,  until  the 
paper  is  just  faintly  reddened.  Now  add  a  drop 
of  ammonia,  then  a  drop  of  acid,  and  so  on,  until 
the  acid  and  alkali  exactly  neutralize  one  another. 
Evaporate  the  liquid,  and  white  crystals  will  form 
which  are  neither  acid  nor  alkaline.  They  consti- 
tute a  salt,  ammonium  nitrate,  which  may  be  re- 
served for  use  in  a  future  experiment. 

The  other  nitrogen  acid  previously  referred  to 
is  unimportant.  It  contains  less  oxygen  than  nitric 
acid,  and  is  named  nitrous  acid.  The  terminations 
ous  and  ic  are  used  in  chemical  nomenclature  to  in- 
dicate lower  and  higher  degrees  of  combination 
respectively.  The  salts  of  nitrous  acid  are  called 
nitrites.  So,  also,  we  have  sulphurous  and  sulphu- 
ric acids,  the  one  forming  sulphites  and  the  other 

*  The  true  significance  of  the  terms  acid,  alkali,  base,  and  salt  will 
be  developed  in  subsequent  chapters.  Exhaustive  definitions  would  be 
inappropriate  here. 


62  INORGANIC  CHEMISTRY. 

sulphates.  The  names  of  salts  derived  from  ous 
acids  end  in  ite,  those  from  ic  acids  in  ate. 

One  of  the  fundamental  principles  of  chemistry 
is  the  law  of  definite  proportions.  This  law  asserts 
that  any  given  chemical  compound  always  contains  pre- 
cisely the  same  elements  in  exactly  the  same  proportions. 
No  variation  is  possible.  When,  however,  two  ele- 
ments unite  to  form  more  than  one  distinct  com- 
pound, the  law  of  multiple  proportions  comes  into 
play.  This  law  is  best  illustrated  by  the  five  oxides 
of  nitrogen,  which  are  composed  by  volume  as  fol- 
lows : 

Nitrogen  monoxide  contains  2  vols.  nitrogen  with  I  vol.  oxygen, 

dioxide  "         "  "          "           "     2    " 

trioxide  "         "  "          "            "     3    " 

tetroxide  "         "  "          "           "     4    " 

pentoxide  "         "  "          "           "     5    " 

We  find  a  similar  regularity  in  their  composition 
by  weight : 

Nitrogen  monoxide  contains  28  parts  of  nitrogen  to  16  of  oxygen. 

dioxide          "         "          "          "          "  32  " 

trioxide          "         "          "          "          "  48  " 

tetroxide        "          "          "          "          "  64  " 

"         pentoxide       "         "          "          "          "  80  "        " 

In  both  tables,  nitrogen  being  constant,  we  see  that 
the  oxygen  varies  in  a  simple  multiple  ratio.  Hence 
the  law,  of  which  many  other  examples  could  be 
cited,  that  when  two  elements  unite  to  form  several 
compounds,  the  higher  proportions  of  each  are  even  mul- 
tiples of  the  lowest. 

Two  of  these  oxides,  the  third  and  the  fifth,  are 
unimportant.  The  fifth  is  a  white,  crystalline,  ex- 
plosive body,  which  reacts  with  water  so  as  to  form 


AMMONIA  AND  THE  OXIDES  OF  NITROGEN.  63 

nitric  acid.  From  the  third,  nitrous  acid  is  simi- 
larly derived.  These  two  compounds  need  no  fur- 
ther notice  here.  The  others  are  more  important. 

Nitrogen  monoxide,  commonly  known  as  ni- 
trous oxide,  is  a  colorless,  odorless,  slightly  sweetish 
gas,  twenty-two  times  heavier  than  hydrogen.  By 
great  cold  and  pressure  it  can  be  liquefied,  and 
even  frozen  solid.  The  only  available  mode  of  prep- 
aration is  as  follows : 

EXPERIMENT  32. — Arrange  a  test-tube  and  deliv- 
ery-tube precisely  as  for  the  preparation  of  oxygen. 
Fill  the  test-tube  half  full  of  dry  ammonium  nitrate 
(see  Experiment  31),  and  heat  very  gradually.  The 
ammonium  nitrate  will  first  melt,  and  then  undergo 
decomposition;  the  products  of  the  latter  change 
being  nitrogen  monoxide  and  water.  The  nitrous 
oxide  can  be  collected  in  a  gas-bag,  or  in  bottles 
over  the  water-pan.  If  the  heating  be  conducted 
too  rapidly,  the  gas  will  be  likely  to  contain  delete- 
rious impurities. 

Although  nitrous  oxide  is  not  really  capable  of 
sustaining  life,  it  may  be  breathed  to  a  limited  ex- 
tent without  danger.  For  this  purpose,  however, 
it  should  be  quite  pure ;  a  condition  best  to  be  se- 
cured by  using  only  materials  of  good  quality,  evolv- 
ing the  gas  very  slowly,  and  washing  it  by  causing 
it  to  bubble  through  several  bottles  of  water  be- 
fore it  reaches  the  gas-bag.  When  inhaled  in  small 
quantities,  nitrous  oxide  produces  a  peculiar  exhila- 
ration, because  of  which  it  has  received  the  popu- 
lar name  of  "  laughing  gas."  Prolonged  inhalation 
leads  to  unconsciousness,  with  complete  insensi- 
bility to  pain.  Hence  its  use  by  dentists  as  an  an- 
aesthetic. 


64  INORGANIC  CHEMISTRY. 

In  nitrous  oxide  the  elements  are  feebly  united. 
Strong  heating,  therefore,  will  decompose  it,  setting 
oxygen  free.  By  virtue  of  this  fact  it  is  capable 
of  supporting  combustion.  Immerse  a  splinter  of 
ignited  charcoal  in  the  gas,  and  it  will  burn  almost 
as  brilliantly  as  in  pure  oxygen.  The  red-hot  coal 
first  decomposes  a  little  of  the  gas;  the  oxygen 
thus  liberated  takes  part  in  the  combustion,  devel- 
oping more  heat ;  this  leads  to  further  decomposi- 
tion, more  oxygen  becomes  free,  and  so  on  to  the 
end  of  the  reaction.  To  verify  this  point,  repeat 
Experiments  12,  13,  and  15,  using  nitrogen  monox- 
ide instead  of  oxygen.. 

Nitrogen  dioxide,  sometimes  called  nitric  oxide, 
is  another  colorless  gas  only  fifteen  times  heavier 
than  hydrogen.  Its  odor  is  extremely  suffocating, 
and  it  supports  combustion  only  in  one  or  two  ex- 
ceptional instances.  It  is  prepared  thus : 

EXPERIMENT  33. — Put  some  copper  scraps  or 
turnings  in  the  flask  previously  used  for  generating 
hydrogen,  and  cover  them  with  a  half-and-half  mix- 
ture of  nitric  acid  and  water.  Connect  the  delivery- 
tube  with  a  glass  jar  full  of  water,  and  inverted  in 
the  usual  way  over  the  water-pan.  At  first,  heavy 
brownish-red  vapors  will  be  evolved,  but  after  a 
few  moments  they  will  disappear,  and  the  jar  will 
fill  with  colorless  nitric  oxide. 

The  most  interesting  property  of  this  gas  is  its 
power  of  absorbing  oxygen.  Lift  the  jar  just  filled 
with  it  so  as  to  admit  the  air,  and  it  will  change  to 
the  deep-red  suffocating  gas  which  was  noticed  at 
the  beginning  of  the  experiment.  This  colored  gas 
is  nitrogen  tetroxide,  or  hyponitric  acid,  and  we 
shall  frequently  encounter  it  in  our  experiments. 


AMMONIA  AND  THE  OXIDES  OF  NITROGEN.  65 

It  appears  whenever  metals  are  dissolved  or  oxi- 
dized by  nitric  acid. 

In  these  experiments  we  have  seen  how  inti- 
mately the  oxides  of  nitrogen  are  connected,  and 
also  that  all  are  derived  either  from  nitric  acid  or 
nitrates.  We  may  now  go  a  step  further  and  obtain 
even  the  strong  base  ammonia  as  a  derivative  of 
nitric  acid,  as  follows  : 

EXPERIMENT  34. — Add  some  zinc  filings  to  a 
strong  solution  of  caustic  potash,  and  heat  the  mix- 
ture in  a  flask,  gently.  Now  put  in  a  little  nitric 
acid,  but  not  so  much  as  to  neutralize  the  alkali. 
Ammonia  will  be  given  off,  and  it  may  be  recog- 
nized by  its  smell.  In  this  experiment  hydrogen  is 
produced  by  the  action  of  the  zinc  upon  the  alkali ; 
and  this,  at  the  instant  of  its  liberation,  so  reacts 
upon  the  nitric  acid  as  to  transform  it  into  ammonia 
and  water. 


CHAPTER   VIII. 

ATOMIC  WEIGHTS  AND   CHEMICAL  FORMULA. 

IN  the  foregoing  chapters  we  have  studied  a 
number  of  compounds,  involving  the  consideration 
of  only  three  elements,  hydrogen,  oxygen,  and  nitro- 
gen. If,  now,  we  scrutinize  their  composition  a  lit- 
tle more  closely,  some  remarkable  relations  may  be 
brought  out. 

To  'facilitate  study,  let  us  begin  by  adopting  a 
set  of  abbreviations  or  symbols,  by  which  the  va- 
rious elements  may  be  concisely  indicated.  Such 
symbols  are  a  necessity  to  the  chemist,  and  to  each 
element  one  is  definitely  assigned.  Thus,  H  repre- 
sents hydrogen,  O  oxygen,  N  nitrogen,  and  C  car- 
bon. Since  several  elements  may  have  names  be- 
ginning with  the  same  initial  letter,  double  letters 
are  frequently  employed,  as  follows  : 

C    represents  carbon, 

Cd  "  cadmium, 

Ca  "  calcium, 

Cs  "  caesium, 

Ce  "  cerium, 

Cl  "  chlorine, 

Cr  "  chromium, 

Co  "  cobalt, 

Cb  "  columbium, 

Cu  "  copper. 


ATOMIC    WEIGHTS,   CHEMICAL  FORMULA.  67 

The  last  of  these  is  derived  from  the  Latin  cu- 
prum. So  also  we  have  Fe,  from  ferrum,  for  iron ; 
Ag,  from  argentum,  for  silver ;  Au,  from  aurum,  for 
gold ;  Sn,  from  stannum,  for  tin ;  and  so  on  in  sev- 
eral other  cases.  These  symbols  should  all  be 
learned  by  actual  use,  rather  than  by  mere  memor- 
izing.* 

Now,  using  these  symbols,  let  us  tabulate  the 
compounds  thus  far  examined  ;  giving  the  compo- 
sition of  each  both  by  volume  and  by  weight : 


By  volume. 


By  weight. 


Water. 

2  vols.  H,  i  vol.  O.     2  parts  H,  16  parts  O. 

Hydrogen  dioxide. 

2 

H,  2 

0.      2 

H,32 

O. 

Ammonia. 

3 

H,  i 

N.     3 

H,  14 

N. 

Nitrogen  monoxide. 

2 

N,  i 

0.  28 

N,  16 

0. 

"        dioxide. 

2 

N,  2 

O.  28 

N,  32 

0. 

"        trioxide. 

2 

N,3 

O.  28 

N,  48 

O. 

"        tetroxide. 

2 

N|4 

0.  28 

N,  64 

0. 

"        pentoxide. 

2 

N,  5 

O.  28 

N,  80 

0. 

Nitrous  acid,  i  vol.  H, 

I 

N,  2 

0.     i 

H,  14 

N, 

32  parts  O. 

Nitric  acid,     i   "    H, 

I 

N,3 

0.     i 

H,  14 

N, 

48    "     0. 

These  numbers  are  very  suggestive,  especially 
when  we  consider  them  in  the  light  of  the  law  of 
multiple  proportions.  Hydrogen  is  represented  by 
i,  2,  and  3  volumes,  or  i,  2,  and  3  parts  by  weight. 
Oxygen  we  find  in  the  proportion  of  i,  2,  3,  4,  and 
5  volumes,  or  16,  32,  48,  64,  and  80  parts  by  weight. 
Nitrogen  occurs  in  i  and  2  volumes,  or  14  and  28 
parts  by  weight.  In  brief,  as  far  as  our  experience 
goes,  if  we  take  hydrogen  as  our  standard  of  com- 
parison and  put  its  combining  value  at  unity,  oxygen 
always  combines  in  the  proportion  of  16  parts  by 
weight  or  some  even  multiple  thereof,  and  nitrogen 
in  the  ratio  of  14  parts  or  a  multiple.  Furthermore, 

*  See  table  of  elements  in  Chapter  II. 


68  INORGANIC  CHEMISTRY. 

these  numbers,  14  and  16,  which  we  may  now  call 
the  combining  weights  of  nitrogen  and  oxygen,  also 
represent  the  specific  gravity  of  these  gases,  referred 
to  hydrogen  as  unity. 

As  we  extend  our  observations  to  the  other 
chemical  elements,  we  shall  find  similar  relations 
holding  good  everywhere.  For  each  element  a 
definite  combining  weight  can  be  found,  which  will 
apply  in  all  the  compounds  into  which  the  element 
can  enter.  For  example : 

i  part  H  unites  with  35.5  parts  Cl. 
i  "  H  "  "  80  "  Br. 
i  "  H  "  "  127  "  I. 

These  values,  35.5,  80,  and  127,  are  the  combining 
weights  of  chlorine,  bromine,  and  iodine  respect- 
ively ;  and  they  also  represent  the  specific  gravity 
of  each  element  in  the  gaseous  state  compared  as 
before  with  hydrogen  as  unity. 

But  many  of  the  elements  do  not  combine  di- 
rectly with  hydrogen,  and  therefore  their  combin- 
ing weights  need  to  be  determined  indirectly.  This 
is  easily  done  through  the  medium  of  some  other 
element ;  thus : 

35.5  parts  Cl  unite  with  23  of  Na,  39  of  K,  or  108  of  Ag. 

80.0     "     Br    "        "     23  "  Na,  39  "  K,  "   108  "  Ag. 

127.0     "     I      "        "     23  "  Na,  39  "  K,  "   1 08  "  Ag. 

Hence  23  may  be  taken  as  the  combining  weight 
of  sodium,  39  of  potassium,  and  108  of  silver;  and 
if  we  go  further  and  examine  the  compounds  of 
these  metals  with  oxygen,  nitric  acid,  etc.,  we  shall 
find  that  the  values  here  assigned  are  in  perfect  har- 
mony with  those  previously  found  for  hydrogen, 


ATOMIC    WEIGHTS,   CHEMICAL  FORMULA.  69 

oxygen,  and  nitrogen.  The  practical  importance  of 
such  numbers  will  appear  as  in  subsequent  chapters 
we  become  familiar  with  their  use.* 

Now,  what  do  these  simple  relations  mean? 
Why  do  we  never  find  oxygen  uniting  in  fifteen  or 
seventeen  parts,  but  always  in  proportions  repre- 
sented by  multiples  of  sixteen  ?  The  answer  to  this 
question  was  discovered  by  Dr.  John  Dalton,  of 
Manchester,  England,  who  put  forth  in  1808  the 
atomic  theory  which  lies  at  the  foundations  of  mod- 
ern chemistry.  If  matter  is,  as  we  have  already 
supposed,  made  up  of  minute,  indivisible  atoms,  it 
is  plain  that  in  chemical  union  only  whole  atoms  and 
multiples  of  whole  atoms  can  take  part.  Fractions 
of  atoms  are  impossible.  If,  then,  hydrogen  and 
oxygen  unite  chemically,  they  must  do  so  in  pro- 
portions representing  either  the  relative  weights  of 
their  atoms,  or  simple  multiples  thereof,  and  similar 
rules  must  govern  the  combination  of  all  the  ele- 
ments. We  assume,  therefore,  that  the  combining 
weights  really  represent  the  relative  weights  of  the 
different  atoms,  compared  with  hydrogen  as  unity. 
That  is,  an  atom  of  oxygen  weighs  sixteen  times  as 
much  as  an  atom  of  hydrogen,  an  atom  of  nitrogen 
fourteen  times  as  much,  an  atom  of  silver  one  hun- 
dred and  eight  times  as  much,  and  so  on.  These 
values  are  called  the  atomic  weights  of  the  elements, 
and  a  full  table  of  them  is  given  in  Chapter  II.  As 
to  the  real  weights  of  the  atoms  we  have  no  defi- 
nite knowledge ;  but  concerning  these  comparative 
weights  we  are  quite  certain.  As  we  continue  our 

*  The  history  of  the  discovery  of  the  combining  weights  is  admira- 
bly given  in  the  earlier  chapters  of  Wurtz's  "Atomic  Theory"  ("  In- 
ternational Scientific  Series,"  vol.  xxix). 


70  INORGANIC  CHEMISTRY. 

studies  we  shall  find  other  lines  of  evidence  confirm- 
ing our  present  conclusions  very  strongly. 

With  the  aid  of  the  elementary  symbols  and 
atomic  weights  we  are  now  ready  to  approach  the 
subject  of  chemical  formulas.  First,  let  us  render 
our  symbols  a  little  more  precise.  Let  H,  for  ex- 
ample, represent  not  only  hydrogen  in  general,  but 
exactly  one  unit  weight  of  hydrogen,  or  one  unit 
volume,  or,  more  definitely  still,  one  atom.  Let  O, 
N,  C,  etc.,  similarly  stand  for  one  atom  of  each  ele- 
ment respectively,  and  for  16,  14,  12,  etc.,  parts  by 
weight,  as  the  case  may  be.  Furthermore,  let  us 
express  several  atoms  of  an  element  by  numerals 
added  to  its  symbol ;  as,  for  example,  H,  H2,  H3,  H4, 
etc.,  for  one  two,  three,  or  four  atoms  of  hydrogen. 
Water,  as  we  have  already  seen,  contains  two 
unit  weights,  or  two  volumes  of  hydrogen,  com- 
bined with  sixteen  unit  weights  or  one  volume  of 
oxygen.  Its  formula,  accordingly,  is  written  H2O  ; 
the  symbols  being  placed  side  by  side  to  indicate 
chemical  union.  Hydrogen  dioxide,  on  like  princi- 
ples, becomes  H2O2,  and  the  nitrogen  compounds  are 
easily  formulated  as  follows : 

Ammonia,  NH3. 

Nitrogen  monoxide,  N2O. 
"         dioxide,       N2O2* 
"         trioxide,      N2O3. 

tetroxide,     N2O4.* 
"         pentoxide,  N2O8. 

Nitrous  acid,  HNO2. 

Nitric      "  HNO3. 

These  formulae  almost  explain  themselves.     For 
example,  let  us  consider  the  last  one,  because  it  is 

*  These  two  formulae  should  be  halved,  becoming  NO  and  NOa 
respectively,  for  reasons  which  will  be  presented  further  on. 


ATOMIC    WEIGHTS,    CHEMICAL   FORMULA,  fi 

the  most  complicated.  It  shows,  first,  that  nitric 
acid  contains  one  atom  of  hydrogen,  one  of  nitro- 
gen, and  three  of  oxygen  combined  together ;  and 
next,  that  the  gases  are  united  by  volume  in  the 
same  ratio  of  i  :  i  :  3.  By  weight  it  indicates  one 
part  of  the  first  element,  fourteen  of  the  second,  and 
three  times  sixteen  of  the  third.  Finally,  just  as  H 
represents  one  atom  of  hydrogen,  so  HNO3  stands 
for  one  molecule  of  nitric  acid,  and  the  sum  of  the 
atomic  weights  i  -f-  14  +  4-8,  or  63,  is  called  the  molecu- 
lar weight  of  the  compound.  If  we  wish  to  indicate 
two  or  more  molecules  of  nitric  acid,  we  may  write 
either  2HNO3,  or  (HNO3)2 ;  but  the  former  method 
is  customary. 

All  such  formulas  as  these  are  capable  of  being 
treated  in  a  somewhat  mathematical  way,  so  that 
chemical  reactions  may  be  written  out  in  the  form 
of  equations.  On  one  side  of  an  equation  we  write 
the  formulas  of  the  substances  with  which  our  re- 
action begins,  and  on  the  other  the  formulas  of  the 
substances  produced  by  the  change.  Thus,  in  mak- 
ing oxygen  we  heat  potassium  chlorate,  KC1O3,  get- 
ting potassium  chloride  and  the  gas  sought  for. 
The  equation  is  simple  : 

KC10,  =  KC1  +  03. 

Again,  ammonium  nitrate,  N2H5O3,  splits  up,  on 
heating,  into  nitrogen  monoxide  and  water,  as  fol- 
lows: 

N3H6O3  =  N2O  +  2H2O. 

Hydrogen  is  commonly  prepared  by  the  action  of  sul- 
phuric acid,  H2SO4,  upon  zinc  ;  zinc  sulphate,  ZnSO4, 
being  also  formed.  This  reaction  we  may  write  : 

Zn  +  H2SO4  =  H2  +  ZnSO4. 


72  INORGANIC  CHEMISTRY. 

It  will  be  noticed  that  the  plus  sign,  -)-,  is  used  to 
indicate  addition,  or  mixture,  as  distinct  from  chemi- 
cal union.  The  minus  sign  is  sometimes  used  also, 
to  represent  the  withdrawal  of  certain  elements 
from  a  compound. 

This  class  of  chemical  equations  has  very  great 
practical  utility,  inasmuch  as  they  enable  us  to  cal- 
culate the  results  of  reactions  in  advance.  Suppose, 
for  instance,  we  wish  to  prepare  a  definite  quantity 
— say  one  pound  or  one  kilogramme  of  nitric  acid 
— and  desire  to  know  just  how  much  material  to 
use  in  order  to  avoid  wasting.  The  reaction  is  as 

follows : 

KNO3  +  H2SO4  =  KHSO4  +  HNO3. 

That  is,  one  molecule  of  potassium  nitrate  and  one 
molecule  of  sulphuric  acid  yield  one  molecule  of 
potassium  hydrogen  sulphate  and  one  molecule  of 
nitric  acid.  Now  the  molecular  weight  of  KNO3  is 
39  +  14  +  48  =  101 ;  that  of  H2SO4  is  2  +  32  +  64  — 
98  ;  and  that  of  HNO3  is  i  +  14  +  48  ==  63.  Hence, 
1 01  parts  of  KNO3,  treated  with  98  of  H2SO4,  will 
give  63  parts  of  HNO3.  For  "  parts "  now  read 
"  pounds,"  "  ounces,"  "  grammes,"  or  "  kilogrammes," 
as  the  case  may  be,  and  the  problem  resolves  itself 
into  an  easy  question  in  arithmetic. 

Again,  let  us  consider  the  preparation  of  oxy- 
gen, for  which  the  equation  has  recently  been  given. 
The  molecular  weight  of  KC1O3  is  39  -j-  35.5  +  48  = 
122.5.  Hence,  122.5  parts  of  KC1O3  yield  48  parts 
of  oxygen.  Suppose  now  we  wish  to  make  exactly 
fifty  litres  of  oxygen,  measured  at  o°  and  760  mm. 
In  Chapter  III  we  found  the  weight  of  one  litre  of 
hydrogen,  or  one  crith,  to  be  0.0896  gramme.  A 
litre  of  oxygen  weighs  16  criths,  and  therefore  fifty 


ATOMIC    WEIGHTS,   CHEMICAL  FORMULAE.  73 

litres  must  weigh  71.68  grammes.  Hence,  by  a  sim- 
ple proportion  — 

48  :  122.5    ::  71.68  :  x,  or, 
O3  :  KC1O3  ::  71.68  :  x, 

in  which  x  represents  the  weight  of  potassium 
chlorate  needed  to  prepare  the  quantity  of  oxygen 
sought  for.  If  our  oxygen  is  to  be  measured  at  a 
temperature  and  pressure  other  than  o°  and  760 
mm.  —  say  at  21°  and  755  mm.  —  we  must  correct  the 
weight  of  our  fifty  litres  by  the  aid  of  the  formulae 
given  in  Chapter  III.  Fifty  litres  of  gas,  at  o°  and 
760  mm.,  will  become  at  21°  and  755  mm.  : 

50  x  760  x  294 


This  quantity,  54.2027  litres,  weighs  the  same  as  be- 
fore —  namely,  71.68  grammes,  and  fifty  litres  of  the 
expanded  gas  will  weigh 

54.2027  :  50  ::  71.68  :  x, 

x  being  the  corrected  weight  of  the  volume  of  oxy- 
gen desired. 

The  department  of  chemistry  which  deals  with 
these  calculations  is  called  stoichiometry.  Many  other 
stoichiometrical  problems  will  be  taken  up  from  time 
to  time  as  we  proceed.* 

*  For  a  good  outline  of  the  principles  of  stoichiometry,  see  Chapter 
VI  of  Cooke's  "  Chemical  Philosophy,"  new  edition,  1881. 


CHAPTER   IX. 

CARBON. 

CARBON,  one  of  the  most  common  and  most  in- 
teresting of  the  elements,  is  found  in  nature  both 
free  and  in  a  vast  number  of  compounds.  It  is  an 
important  constituent  of  limestone  and  many  min- 
erals ;  it  forms  great  beds  of  coal ;  it  is  the  element 
chiefly  characteristic  of  animal  and  vegetable  mat- 
ter. Chemistry  is  commonly  divided  into  two  great 
branches — injorganic  and  organic ;  the  former  deal- 
ing with  substances  formed  in  inanimate  nature,  the 
latter  with  the  products  of  organic  life  and  their 
derivatives.  At  present,  organic  chemistry  is  usu- 
ally denned  as  "  the  chemistry  of  the  carbon  com- 
pounds," and  as  such  it  might  be  fairly  considered 
here.  For  convenience,  however,  organic  chemis- 
try will  be  discussed  separately  later  on ;  and  in 
this  chapter  we  may  limit  ourselves  to  carbon  in 
some  of  its  inorganic  aspects. 

Carbon  itself  is  one  of  the  best  examples  of  allo- 
tropy,  since  it  occurs  in  three  distinct  forms — name- 
ly, as  diamond,  as  graphite,  and  as  charcoal.  In  all 
of  its  forms  it  is  tasteless,  odorless,  infusible,  non- 
volatile, and  insoluble.  It  is,  however,  combustible ; 
readily  so  as  charcoal,  more  difficultly  in  its  other 
modifications.  But  even  the  diamond  burns  in  the 


CARBON. 


75 


oxyhydrogen-flame.     The  atomic  weight  of  carbon 
is  12. 

The  diamond  is  found  in  India,  Borneo,  South 
Africa,  and  Brazil ;  and  occasionally  in  North  Caro- 
lina, Georgia,  and  California.  It  occurs  in  crystals, 
more  or  less  perfect,  derived  from  the  regular  octa- 
hedron (Fig.  19),  and  has  in  its  purest  state  a  spe- 
cific gravity  of  3.518.  In  color  it  ranges  from  a 
pure  limpidity  well  described  in  the  phrase  "  a  gem 


FIG.  19. — Crystals  of  Diamond. 

of  the -first  water"  through  various  shades  of  yellow, 
blue,  green,  pink,  etc.,  to  black.  Generally  the  col- 
orless stones  are  most  prized,  the  yellow  diamonds 
being  of  much  less  value.  Occasionally  a  blue  or 
green  diamond  brings  an  enormous  price,  for  these 
tints  are  very  rare.  The  black  variety  is  called  car- 
bonado, and  has  a  slightly  lower  specific  gravity. 

The  diamond  refracts  light  very  strongly,  and  to 
this  property  it  owes  its  brilliancy  as  a  gem.  It  is 
the  hardest  of  all  known  substances,  and  can  be  cut 
and  polished  only  with  its  own  powder.  Because 
of  its  hardness  it  is  used  for  cutting  glass ;  and  the 
coarser  varieties,  such  as  carbonado,  serve  to  tip  the 
diamond-drills  which  are  now  employed  in  rock- 


76  INORGANIC  CHEMISTRY. 

boring  machinery.  In  1880  small  diamonds  were 
produced  artificially  by  Mr.  J.  B.  Hannay,  of  Glas- 
gow ;  but  the  details  of  the  process  have  only  par- 
tially been  made  public. 

Graphite,  also  known  as  plumbago  or  black-lead, 
is  extensively  mined  in  England,  Ceylon,  Siberia, 
and  California,  and  at  Ticonderoga  in  New  York. 
There  are  many  other  localities  in  which  it  is  found, 
so  that  it  may  fairly  be  reckoned  one  of  the  com- 
moner minerals.  It  occurs  in  some  meteorites,  and 
it  is  frequently  produced  in  the  blast-furnace.  In 
the  latter  case  it  is  dissolved  by  the  molten  iron, 
and  crystallizes  out  upon  cooling.  It  differs  from 
the  diamond  in  many  particulars ;  its  color  is  black, 
its  specific  gravity  about  2.15,  and  it  crystallizes  in 
six-sided  plates.  It  is  a  good  conductor  of  heat  and 
electricity,  whereas  the  diamond  conducts  badly. 
It  may  be  more  easily  burned  than  diamond,  less 
easily  than  charcoal.  In  fine  powder  it  has  a  greasy 
feel,  and  is  somewhat  used  as  a  lubricant  for  ma- 
chinery. It  is  chiefly  used  in  the  manufacture  of 
lead-pencils,  stove-polish,  and  crucibles,  as  a  con- 
ductor of  electricity  in  the  process  of  electrotyp- 
ing,  and  as  a  glazing  for  the  grains  of  gunpowder. 
Gold  and  silver  are  usually  melted  in  black-lead 
crucibles.  In  the  manufacture  of  coal-gas,  a  very 
hard  coating  of  gas-carbon  is  formed  in  the  gas-re- 
torts. This  is  commonly  regarded  as  a  variety  of 
graphite,  and  is  used  in  the  Bunsen  galvanic  bat- 
tery, and  for  making  the  carbon-points  of  the  elec- 
tric light. 

Amorphous  (shapeless  or  non-crystalline)  carbon 
is  always  of  organic  origin.  As  charcoal  it  is  pro- 
duced by  the  imperfect  combustion  of  wood,  retain- 


CARBON.  77 

ing  the  structure  of  the  latter  almost  perfectly.  A 
purer  charcoal  may  be  prepared  by  heating  pure 
white  sugar.  Another  variety,  lamp-black,  is  made 
by  burning  tar,  rosin,  turpentine,  or  petroleum,  with 
a  deficient  supply  of  air,  and  passing  the  smoke  into 
large  chambers,  in  which  the  carbon  is  deposited. 
It  is  simply  soot  prepared  on  a  large  scale,  and  it  is 
used  as  a  black  paint  and  for  making  printer's  ink. 
India  ink  is  also  made  from  lamp-black  Animal 
charcoal,  as  its  name  suggests,  is  produced  by  char- 
ring animal  matter  in  close  iron  cylinders,  The 
finest  quality  is  made  from  blood,  but  bone-black, 
containing  with  the  carbon  the  earthy  constituents 
of  bones,  is  more  extensively  prepared. 

In  all  of  its  varieties  amorphous  carbon  is  black, 
and  easily  combustible.  Its  specific  gravity  ranges 
from  1.57  to  2.00;  the  variability  resulting  from  the 
fact  that  charcoal  is  always  more  or  less  porous. 
This  porosity  confers  upon  charcoal  an  extraordi- 
nary power  of  absorbing  gases,  to  which  property 
its  value  as  a  disinfectant  is  due.  For  example,  one 
cubic  centimetre  of  freshly-burned  charcoal  will  ab- 
sorb 17.9  cc.  of  oxygen,  67.7  cc.  of  carbonic  acid,  or 
171.7  cc.  of  ammonia.  Insert  a  bit  of  charcoal  in  a 
tube  of  ammonia-gas  filled  over  mercury,  and  an 
immediate  rise  of  the  latter  in  the  tube  will  indicate 
the  absorption.  Suppose  now  that  a  quantity  of 
charcoal  be  brought  into  an  atmosphere  contami- 
nated with  the  noxious  gases  resulting  from  a  leaky 
sewer  or  from  animal  decomposition.  They  will  at 
once  be  absorbed;  and,  coming  into  close  contact  with 
oxygen  which  has  been  absorbed  also,  they  will  be 
oxidized  and  rendered  harmless.  The  vigor  of  this 
action  may  be  shown  by  the  following  experiment: 


78  INORGANIC  CHEMISTRY. 

EXPERIMENT  35. — Heat  a  fragment  of  charcoal 
to  redness,  so  as  to  expel  whatever  gases  it  may  con- 
tain, and  allow  it  to  cool  under  mercury.  Now 
plunge  it  into  a  jar  of  sulphuretted  hydrogen  (Chap- 
ter XV),  and  after  a  few  moments  transfer  it  to  an- 
other vessel  containing  oxygen.  The  two  condensed 
gases,  meeting  in  the  pores  of  the  charcoal,  will  unite 
with  such  intensity  that  the  carbon  will  at  once  in- 
flame. 

The  same  principle  may  receive  a  number  of 
other  less  startling  but  more  practical  illustrations. 
Rub  a  little  powdered  charcoal  upon  tainted  meat, 
and  the  unpleasant  smell  will  disappear.  Water 
frequently  has  a  fetid  odor  derived  from  organic 
impurities ;  this  may  be  corrected  by  simply  filter- 
ing the  water  through  a  thick  layer  of  charcoal.  So, 
also,  by  charring  the  lower  end  of  a  fence-post  or 
telegraph-post,  it  may  be  protected  to  a  considerable 
extent  from  rotting. 

Charcoal  also  has  a  very  remarkable  power  of 
absorbing  coloring  -  matters  and  many  other  sub- 
stances. Animal  charcoal  is  extensively  used  in 
sugar-refineries  for  decolorizing  raw  brown  sugar 
and  converting  it  into  the  finer  white  varieties.  A 
simple  experiment  will  serve  to  illustrate  this  prop- 
erty : 

EXPERIMENT  36.— Half  fill  a  small  bottle  with 
red  wine,  a  solution  of  indigo,  or  a  solution  of  cochi- 
neal, and  add  an  equal  bulk  of  freshly-burned  char- 
coal-powder. Bone-black  is  better  still  if  it  can  be 
obtained.  Shake  vigorously,  and  filter ;  the  filtrate 
will  be  colorless  or  nearly  so.  Beer  or  ale,  similarly 
treated,  loses  both  its  color  and  its  bitterness.  Even 
a  solution  of  quinine  may  be  rendered  nearly  taste- 


CARBON. 


79 


less  by  filtering  through  charcoal,  the  quinine  being 
absorbed  and  retained. 

Coke  is  a  variety  of  amorphous  carbon  which 
remains  behind  after  coal  has  been  heated  for  the 
manufacture  of  illuminating  gas.  Coal  itself  is  very 
impure  carbon,  containing  various  compounds  of 
hydrogen,  together  with  nitrogen,  oxygen,  sulphur, 
and  the  various  earthy  substances  which  constitute 
the  ash.  It  varies  much  in  composition,  as  the  fol- 
lowing percentage  analyses  show  :  * 


Anthracite. 

Soft  coal. 

Cannel-coal. 

Lignite. 

Carbon  

Q2.SQ 

80.33 

80.07 

66.31 

Hydrogen 

2.63 

4.4.7 

C.C7, 

5.63 

Oxygen  

^.WJ 

1.61 

3.25 

8.10 

22.86 

Nitrogen 

O.Q2 

1.24. 

2.IO 

O.  C7 

Sulphur  

o.^s 

1.  10 

WO/ 
2.36 

Ash 

2  2? 

1.  2O 

2  7O 

2  27 

100.00 

IOO.OO 

IOO.OO 

100.00 

The  compounds  of  carbon  with  hydrogen,  the  hy- 
drocarbons, are  very  numerous,  and  are,  in  general, 
of  organic  origin.  Coal-oil  and  petroleum  are  vari- 
able mixtures  of  hydrocarbons ;  and  the  hydrogen 
of  coal  exists  partly  combined  with  carbon  and 
partly  in  the  form  of  water.  Since  the  value  of 
coal  for  the  manufacture  of  gas  depends  upon  the 
hydrocarbons  which  it  contains,  two  or  three  of 
these  compounds  may  fittingly  be  described  here, 
while  the  others  will  be  considered  in  connection 
with  organic  chemistry,  further  on. 

Methane,f  also  known  as  marsh-gas,  fire-damp, 

*  In  Dana's  "  System  of  Mineralogy  "  a  large  number  of  coal  analy- 
ses are  given.  The  variations  are  extraordinary. 

f  The  naming  of  the  hydrocarbons  is  somewhat  arbitrary.  This 
point  will  be  considered  under  organic  chemistry. 


8o 


INORGANIC  CHEMISTRY. 


and  light  carbureted  hydrogen,  is  a  colorless  gas 
having  the  formula  CH4.  It  burns  readily  with  a 
bluish-yellow  flame,  emitting  much  heat  and  but  lit- 
tle light.  In  nature  it  is  often  produced  by  the  slow 
decay  of  dead  leaves  at  the  bottoms  of  stagnant 
pools ;  hence  the  common  name,  marsh-gas.  By 
stirring  up  the  mud  beneath  a  jar  of  water  inserted 
in  such  a  pool,  the  bubbles  of  gas  may  be  collected 
and  identified  (Fig.  20).  It  also  frequently  accumu- 
lates in  coal-mines,  forming  a  dangerously  explosive 


FIG.  20. — Collection  of  Marsh-gas. 

mixture  with  the  oxygen  of  the  air.  Such  mixtures, 
ignited  by  miners'  lamps,  have  caused  terrible  loss 
of  life.  Fire-damp  is  the  miner's  name  for  the  gas, 
distinguishing  it  from  the  suffocating  carbonic  acid, 
or  choke-damp.  It  sometimes  issues  in  great  quanti- 
ties from  the  earth,  and  particularly  from  artesian 
wells  sunk  in  search  of  petroleum.  In  some  such 


CARBON.  8 1 

places  it  serves  as  a  fuel,  for  driving  steam-engines ; 
and  the  town  of  Fredonia,  New  York,  is  mainly 
lighted  by  gas  of  natural  origin,  Methane  is  artifi- 
cially prepared  as  follows : 

EXPERIMENT  37. — Mix  thoroughly  two  parts  of 
crystallized  sodium  acetate,  four  parts  of  caustic 
soda,  and  eight  parts  of  powdered  quicklime.  Heat 
gently  on  an  iron  plate  until  the  mixture  is  thor- 
oughly dry  and  crumbly.  Then  heat  it  strongly  in 
a  glass  tube,  such  as  was  used  for  the  preparation  of 
oxygen,  and  collect  the  gas  over  water.  Test  its 
inflammability  as  in  the  case  of  hydrogen.  In  this 
experiment  the  lime  merely  serves  to  render  the 
mass  more  porous,  and  to  protect  the  glass  from  ex- 
cessive corrosion  by  the  caustic  soda.* 

Ethylene,  C2H4,  is  another  gaseous  hydrocarbon 
of  great  importance.  It  is  fourteen  times  heavier 
than  hydrogen,  whereas  the  density  of  methane  is 
only  eight.  Hence  the  old  names  of  heavy  and  light 
carburetted  hydrogen  respectively.  It  is  easily  pre- 
pared by  heating  together  alcohol  and  strong  sul- 
phuric acid,  and  it  burns  with  a  luminous,  smoky 
flame.  It  is  also  known  as  ethene  and  as  olefiant 
(oil-producing)  gas.  The  last  name  was  given  it  be- 
cause it  unites  directly  with  another  gas,  chlorine, 
to  form  an  oily  liquid. 

Acetylene,  C2H2,  is  another  gas,  of  a  disagreeably 
pungent  odor,  which  is  formed  by  the  direct  union 
of  its  elements.  When  a  series  of  powerful  electric 
sparks  are  passed  between  two  carbon-points  in  an 

*  A  cheaper  way  of  preparing  impure  methane  is  to  soak  lumps  of 
lime  in  vinegar,  and  then  to  heat,  as  above,  the  mixture  of  lime  and 
calcium  acetate  thus  obtained.  In  this  process  a  good  deal  of  steam 
is  first  given  off. 


82  INORGANIC  CHEMISTRY. 

atmosphere  of  hydrogen,  acetylene  is  produced.  It 
combines  directly  with  hydrogen  to  form  ethylene ; 
thus  :  C2H2  +  H2  =  C2H4.  It  also  unites  with  cer- 
tain metals,  such  as  copper  or  silver,  yielding  explo- 
sive compounds  of  considerable  interest.  It  burns 
with  a  blue  flame.  All  the  hydrocarbons  burn  more 
or  less  readily,  and  all  form  upon  complete  combus- 
tion only  carbonic  acid  and  water.  For  example : 

CH4  +  O4  =  CO,  +  ?H2O. 
C2H4  +  O6  =  2COa  +  2H2O. 
CaHa  +  O6  =  2CO3  +  H2O. 

By  the  imperfect  combustion  of  hydrocarbons,  acety- 
lene is  often  produced  ;  for  example,  when  a  candle 
burns  with  a  smoky  flame  its  peculiar  odor  may  be 
detected. 

Ordinary  illuminating  gas,  distilled  from  coal,  is 
essentially  a  mixture,  more  or  less  impure,  of  hydro- 
gen, carbon  monoxide,  methane,  and  ethylene.  Its 
production  on  a  small  scale  may  be  illustrated  by  an 
easy  experiment. 

EXPERIMENT  38. — Fill  the  bowl  of  a  common 
clay  tobacco-pipe  with  powdered  soft  coal,  and  cover 
the  latter  tightly  with  a  plug  of  clay.  Heat  the 
bowl  to  redness  over  a  Bunsen  gas-flame  or  between 
the  bars  of  a  grate.  Gas  will  issue  from  the  stem, 
where  it  may  be  ignited. 

In  manufacturing  gas  on  a  large  scale,  bitumi- 
nous or  cannel  coal  is  heated  in  retorts  of  fire-clay  or 
fire-brick  which  hold  from  one  to  two  hundred  pounds 
at  a  time.  Several  retorts  are  heated  at  once  over  a 
single  fire,  and  the  products  of  distillation  pass  out 
into  a  series  of  pipes  in  which  water,  coal-tar,  am- 
monia, etc.,  are  deposited.  The  tar  and  ammonia, 


CARBON.  83 

being  valuable,  are  thus  saved.  Twenty-five  years 
ago  the  tar  was  worthless ;  now  it  serves  as  a  source 
of  benzene,  and  of  the  superb  aniline  dyes.  The 
gas  itself  still  contains  a  number  of  objectionable  im- 
purities, which  are  removed  by  passing  it  over  some 
absorbent  substance,  such  as  slaked  lime.*  Differ- 
ent samples  of  gas  differ  widely  in  composition  ;  the 
differences  depending  upon  the  quality  of  the  coal 
employed,  the  degree  of  heat  applied  to  the  retorts, 
and  so  on.  In  percentages,  the  following  figures  may 
represent  a  fair  average  : 

Hydrogen,  50 

Methane,  35 

Carbon  monoxide,  7 

Ethylene,  3 

Several  impurities,  5 


100 


In  Germany,  gas  is  sometimes  distilled  from 
wood ;  and  in  our  own  country  there  are  processes 
in  use  which  generate  hydrogen  from  steam  and 
charge  it  with  vapors  from  petroleum.  The  latter 
give  its  flame  illuminating  power.  In  ordinary  gas 
the  illuminating  value  depends  mainly  upon  the 
ethylene  which  it  contains. 

If  we  study  a  gas-flame  closely  we  shall  find  that 
its  structure  illustrates  some  important  facts  relat- 
ing to  the  mechanism  of  combustion.  In  a  common 
burner  the  gas  issues  from  a  fine  jet,  and  is  ignited 
in  contact  with  a  moderate  amount  of  air  (Fig.  21). 
Near  the  jet  we  have  a  stream  of  gas  not  yet  burned ; 
and  here  the  flame  is  comparatively  cool  and  non- 

*  A  good  account  of  the  manufacture  and  purification  of  coal-gas  is 
given  in  Roscoe  and  Schorlemmer's  "  Treatise  on  Chemistry,"  vol.  i, 
pp.  683-704. 


84  INORGANIC  CHEMISTRY. 

luminous.     Insert  a  piece  of  slender  glass  tubing  at 
this  part  of  the  flame,  and  the  unburned  gas  may  be 


FIG.  21. — Structure  of  Common  Gas-flame. 

drawn  off  and  kindled  at  the  farther  end  (Fig.  22). 
Above,  and  somewhat  around  this  darker  base,  we 
have  the  luminous  portion  of  the  flame ;  and  here 
the  light  is  partially  due  to  imperfect  combustion. 
Hold  a  piece  of  cold  porcelain  over  the  jet  for  a 
moment,  and  soot  (that  is,  carbon)  will  be  deposited 
upon  it.  It  is  these  solid  particles  in  the  flame  which 
become  heated  and  luminous,  and  they  result  from 
the  partial  combustion  of  ethylene  and  some  of  its 
related  hydrocarbons.  Methane  yields  no  free  car- 
bon under  like  circumstances,  and  of  course  hydro- 
gen does  not;  hence  their  flames,  containing  only 
gaseous  matter,  are  non-luminous.*  If  we  do  any- 

*  In  Experiment  7  the  luminosity  of  a  hot  solid  in  a  hydrogen-flame 
was  illustrated. 


CARBON. 


thing  to  cut  off  the  supply  of  air  from  a  flame,  it  will 
become  fuller  of  carbon-particles  and  more  smoky  ; 
a  fact  which  may  easily  be  verified  by  sliding  a  piece 


FIG.  22. — Withdrawal  of  Gas  from  a  Flame-centre. 

of  sheet-iron  or  other  convenient  solid  over  the  top 
of  a  gas  or  kerosene  lamp-chimney.     As  the  air  is 


FIG.  23. — Bunsen  Burner. 


86 


INORGANIC  CHEMISTRY. 


gradually  excluded,  smoke  and  soot  will  form  copi- 
ously. Conversely,  if  we  render  combustion  more 
perfect,  and  so  prevent  the  deposition  of  carbon,  a 
flame  will  become  hotter  but  less  brilliant.  This  is 
done  in  the  Bunsen  burner  (Fig.  23),  in  which  air  is 
allowed  to  enter  at  the  base  and  become  thoroughly 
mixed  with  the  gas  before  the  latter  is  lighted.  The 
flame  here  emits  very  little  light ;  but  if  the  holes  at 
the  base  are  stopped  up,  then  it  becomes  luminous 
as  usual.  The  Bunsen  burner  is  the  most  conven- 
ient source  of  heat  for  the  minor  operations  of  the 
laboratory.  Where  gas  can  not  be  had,  an  alcohol 
lamp  is  commonly  used  instead.  Such  a  lamp  is 
easily  improvised  by  perforating  the  cork  of  a  small, 
wide-mouthed  bottle,  and  inserting  through  the  per- 
foration a  glass  tube  carrying  a  wick  (Fig.  24). 


FIG.  24. — Improvised  Spirit  Lamp. 

In  the  mouth  blow-pipe  we  have  another  illustra- 
tion of  the  foregoing  principles.     By  the  aid  of  this 


CARBON.  87 

little  instrument  air  is  blown  from  the  cheeks  into  a 
flame,  and  the  latter  is  rendered  much  hotter  (Fig. 
25).  Here,  again,  the  flame  may  be  divided  into 
two  chief  parts ;  an  inner  blue  cone  and  an  outer 


FIG.  25. — Use  of  Blow-pipe. 

portion.  The  greatest  heat  is  at  the  apex  of  the  in- 
ner flame.  A  bit  of  tin  or  zinc,  heated  in  the  outer 
part  of  the  jet,  is  first  melted  and  then  converted 
into  oxide  ;  hence  the  name  of  oxidizing  flame.  On 
the  other  hand,  the  oxide  so  formed,  if  heated  in  the 
inner  cone,  will  be  reduced  to  the  metal  again,  giv- 
ing up  its  oxygen  to  assist  in  the  burning  of  the  car- 
bonaceous matter  there  found.  This  part  of  the  jet, 
therefore,  is  called  the  reducing  flame.  Both  parts 
of  the  flame  are  important  agents  in  blow-pipe  analy- 
sis ;  and  a  little  practice  in  heating  bits  of  copper, 
tin,  zinc,  lead,  etc.,  supported  on  pieces  of  charcoal, 
first  in  one  and  then  in  the  other,  will  make  the  re- 
lations of  the  two  very  clear.  The  stream  of  air 
from  the  blow-pipe  should  be  made  as  steady  as  pos- 
sible ;  and  one  can  easily  learn  to  blow  lightly  from 
the  muscles  of  the  cheeks  for  several  minutes  at  a 
time  without  interrupting  respiration.  The  flame 

5 


88  INORGANIC  CHEMISTRY. 

of  a  lamp  burning  some  animal  or  vegetable  oil  (lard, 
whale,  or  rape-seed  oil,  for  examples),  is  best  for  blow- 
pipe work ;  but  alcohol  or  gas  may  be  used.  Kero- 
sene is  unavailable,  because  the  chimney  interferes. 

In  a  strictly  scientific  sense  a  candle-flame  is  as 
truly  a  gas-flame  as  any  that  issues  from  the  tip 
of  a  gas-burner.  The  wick,  loosely  made  of  cotton 
threads,  is  first  kindled  ;  and  the  heat  thus  gener- 
ated melts  a  small  quantity  of  the  fat,  wax,  or  paraf- 
fine  of  which  the  candle  is  constructed.  The  liquid 
oil  thus  produced  is  drawn  up  into  the  wick  by 
capillary  attraction ;  it  is  decomposed  by  the  heat, 
and  the  gaseous  products  of  decomposition  then 
burn,  depositing  particles  of  carbon  which  become 
luminous.  These  may  be  collected  as  soot ;  and  by 
means  of  a  glass  tube  the  gas  from  the  center  of  the 
flame  can  be  drawn  off  and  ignited.  If  a  sheet  of 
clean  white  cardboard  be  suddenly  pressed  down 
upon  a  candle-flame  and  then  withdrawn,  it  will  be 
found  scorched  in  a  ring,  thus  showing  that  at  the 
center  of  the  flame  there  was  no  active  combustion. 

When  bituminous  coal  is  burned  in  a  furnace, 
the  laws  of  combustion  should  be  carefully  consid- 
ered. A  smoky  chimney  always  means  imperfect 
combustion  and  waste  of  carbon;  and  smoke-pre- 
venting appliances,  the  so-called  "  smoke-consum- 
ers," are  getting  to  be  more  and  more  used  in  cities 
where  soft  coal  is  the  chief  fuel.  Many  such  appli- 
ances have  been  patented,  but  all  aim  at  the  same 
result — namely,  to  bring  about  perfect  combustion. 
Sometimes,  fine  jets  of  steam  are  blown  into  the 
furnace.  These  are  decomposed  at  first,  yielding 
oxygen  and  hydrogen,  which  serve  to  make  the  fire 
more  intense.  In  other  cases  the  coal  is  applied  in 


CARBON.  •    89 

such  a  way  that  the  smoke  from  the  fresh  portions 
of  fuel  is  conducted  over  glowing  beds  of  coke,  the 
latter  being  merely  the  earlier  charges  from  which 
the  sooty  hydrocarbons  have  been  burned  away. 
In  some  metallurgical  furnances  the  fuel  is  rendered 
gaseous  at  the  start,  and  the  gases  are  then  burned 
with  abundance  of  air.  Such  furnaces  give  great 
heat  and  waste  little  or  no  fuel. 

For  every  combustible  substance  there  is  a  defi- 
nite temperature  below  which  it  will  not  ignite.  If 
a  flame  be  cooled  below  the  ignition- 
point  of  the  gas  which  forms  it,  it  will 
go  out.  Press  a  piece  of  wire  gauze 
down  upon  a  gas-flame,  and  the  latter 
will  be  flattened  ;  it  can  not  penetrate 
the  metallic  net-work.  The  gas  itself 
passes  through,  but  the  wire  has  con- 
ducted so  much  heat  away  from  it  that 
combustion  is  no  longer  possible.  You 
can  hold  the  gauze  over  a  jet  of  gas 
and  kindle  the  latter  above,  but  the 
flame  can  not  then  descend  to  the  burn- 
er. Or,  you  may  hold  two  pieces  of 
gauze  parallel  to  each  other  over  a  FIG.  26.— Da- 
stream  of  gas,  and  produce  a  flame  be- 
tween  them  which  shall  be  unable  to 
pass  either  above  or  below.  These  facts  find  their 
application  in  the  safety-lamp  of  Sir  Humphry 
Davy  (Fig.  26).  This,  which  was  invented  for  the 
protection  of  coal-miners  against  fire-damp,  is  mere- 
ly a  lamp  inclosed  in  a  netting  of  fine-wire  gauze. 
This  inclosure  may  be  filled  with  flame,  but  the 
latter  can  not  penetrate  its  prison-walls  and  ignite 
the  explosive  gaseous  mixture  without. 


CHAPTER  X. 

CARBON — (continued}. 

CARBON  unites  with  oxygen  in  two  proportions, 
forming  a  monoxide,  CO,  and  a  dioxide,  CO2. 

Carbon  monoxide,  more  commonly  known  as 
carbonic  oxide,  is  a  colorless,  odorless  gas  which 
burns  with  a  blue  flame.  It  is  not  produced  by  the 
direct  union  of  its  elements  ;  for  when  carbon,  either 
as  diamond,  graphite,  or  charcoal,  is  burned,  only 
carbon  dioxide  is  formed.  By  passing  the  latter, 
however,  over  red-hot  coals,  half  of  its  oxygen  may 
be  withdrawn,  and  carbon  monoxide  results  from 

the  change : 

C02  +  C  =  2CO. 

This  often  happens  in  coal-stoves  and  furnaces,  es- 
pecially in  the  blast-furnace ;  carbon  dioxide  being 
produced  by  the  combustion  of  the  lowest  layer  of 
fuel,  and  rising  through  the  glowing  coals  above. 
The  blue  flames  which  play  over  the  surface  of  an 
anthracite-fire  are  due  to  carbon  monoxide,  and  the 
product  of  the  combustion  is  CO2 : 

CO  +  O  =  C02. 

Carbon  monoxide  may  be  artificially  prepared 
by  various  processes;  but  most  conveniently  by 
heating  either  crystallized  oxalic  acid  or  potassium 


CARBON.  9! 

ferrocyanide  with  strong  sulphuric  acid.  By  the 
reaction  which  ensues,  both  oxides  of  carbon  are 
formed  ;  but,  by  passing  the  mixed  gases  through  a 
solution  of  caustic  potash,  the  dioxide  may  be  ab- 
sorbed, leaving  the  monoxide  pure. 

The  preparation  of  carbon  monoxide  should  be 
undertaken  only  with  extreme  care,  because  the  gas 
is  dangerously  poisonous.  A  trace  of  it  in  the  air 
we  breathe  will  produce  headache  and  dizziness, 
and  anything  over  one  percent  admixture  might 
prove  fatal.  It  sometimes  escapes  from  badly-con- 
structed stoves  into  improperly-ventilated  rooms, 
and  causes  serious  annoyance.  Cheap  cast-iron 
stoves  are  especially  liable  to  work  this  kind  of 
mischief,  and  deaths  have  resulted  from  the  careless 
use  of  such  stoves  in  close  sleeping-apartments. 
All  illuminating  gas  made  from  coal  contains  car- 
bon monoxide  as  one  of  its  ingredients. 

The  other  oxide  of  carbon,  carbon  dioxide,  is 
met  with  under  a  great  variety  of  conditions.  We 
find  it  ever  present  in  the  atmosphere ;  it  is  always 
produced  when  carbon  or  compounds  of  carbon  are 
burned  ;  we  exhale  it  from  our  lungs ;  it  is  evolved 
from  decaying  animal  and  vegetable  matter;  and 
we  recognize  it  among  the  products  of  fermenta- 
tion. 

EXPERIMENT  39. — Cover  the  bottom  of  a  glass 
jar  with  lime-water,*  and  suspend  over  it  a  burning 
bit  of  candle.  Close  the  jar,  and  the  candle  will 
soon  burn  itself  out.  Now  shake  vigorously,  and 
the  lime-water  will  become  milky.  Upon  standing, 

*  Prepared  by  stirring  powdered  lime  into  water,  leaving  the  mix- 
ture to  stand  for  at  least  an  hour,  and  then  filtering.  The  solution 
should  be  perfectly  clear. 


92  INORGANIC  CHEMISTRY. 

the  milkiness  will  be  deposited  as  a  white  sediment. 
This  sediment  is  calcium  carbonate  (carbonate  of 
lime),  and  its  formation  proves  the  presence  of  car- 
bon dioxide  in  the  air  of  the  jar.  A  piece  of  wood 
or  charcoal  burned  in  place  of  the  candle  will  give 
the  same  result. 

EXPERIMENT  40. — Pour  some  lime-water  into  a 
tumbler,  and  through  a  piece  of  glass  tubing  blow 
air  into  the  liquid  for  several  minutes  from  the 
lungs.  The  lime-water  will  become  milky,  showing 
that  carbon  dioxide  has  been  exhaled. 

EXPERIMENT  41. — Mix  in  any  convenient  vessel 
some  very  sweet  molasses-and-water  with  a  little 
yeast.  Fill  a  test-tube  with  the  mixture,  invert  it  in 
the  liquid,  and  let  the  whole  stand  in  a  warm  place 
overnight.  Fermentation  will  occur,  and  bubbles  of 
carbon  dioxide  will  rise  into  the  tube.  Close  the 
mouth  of  the  latter  with  the  thumb,  remove  it  from 
the  vessel,  and  shake  up  its  gaseous  contents  with 
lime-water. 

EXPERIMENT  42. — In  the  same  flask  and  appa- 
ratus which  previously  served  for  the  preparation 
of  hydrogen,  put  some  fragments  of  chalk,  lime- 
stone, or  marble,  and  pour  over  them  a  quantity  of 
dilute  hydrochloric  or  sulphuric  acid.  Gas  will  be 
given  off  with  brisk  effervescence ;  and  by  passing 
a  few  bubbles  of  it  into  lime-water  it  may  be  identi- 
fied as  carbon  dioxide.  Collect  the  remainder  of 
the  gas  as  usual  in  bottles  or  jars  over  the  water-pan. 

The  last  experiment  illustrates  the  only  method 
by  which  carbon  dioxide  is  practically  prepared 
for  use  in  the  laboratory,  The  limestone,  chalk,  or 
marble  is  calcium  carbonate,  CaCO3 ;  and  the  reac- 
tion, when  sulphuric  acid  is  used,  is  as  follows : 


CARBON.  93 

CaCO3  +  H2SO4  =  CaSO*  -I-  HaO  +  CO3. 

That  is,  calcium  carbonate,  treated  with  sulphuric 
acid,  yields  calcium  sulphate,  carbon  dioxide,  and 
water.  Any  other  carbonate  will  give  a  similar  re- 
action with  any  strong  acid,  and  carbon  dioxide  will 
be  evolved  in  the  same  way.  For  example,  pour 
vinegar  (acetic  acid)  over  common  saleratus  (a  car- 
bonate of  sodium),  and  note  the  effervescence.  As 
the  name  indicates,  a  carbonate  is  a  salt  formed  by 
carbonic  acid  with  a  base.  Since  carbonic  acid  is  a 
very  weak  acid,  any  stronger  acid  can  expel  it  from 
its  salts,  as  in  the  foregoing  reactions.  When  free, 
its  formula  should  be  H2CO3,  but  it  is  incapable  of 
existing  independently,  and  therefore  splits  up  at 
the  moment  of  its  liberation  into  carbon  dioxide 
and  water,  CO2  -f  H2O.  Many  carbonates  are  easily 
decomposed  by  heat ;  for  instance,  lime,  which  is 
calcium  oxide,  is  made  by  burning  limestone  in  a 
kiln,  when  carbon  dioxide  is  evolved  freely  : 

CaCO3  =  CaO  +  CO2. 

The  lime  and  carbon  dioxide  thus  separated  can  be 
made  to  unite  again  only  through  the  intervention 
of  water;  the  necessary  reaction  being  one  which 
we  have  already  observed  in  several  experiments. 
Filter  off  some  of  the  sediment  formed  by  carbon 
dioxide  in  lime-water,  and  test  it  with  a  drop  of  any 
common  acid.  It  will  effervesce,  thereby  revealing 
its  character  as  a  carbonate.  Carbon  dioxide  is  fre- 
quently miscalled  carbonic  acid  ;  indeed,  "  carbonic- 
acid  gas  "  is  the  commonest  of  its  names. 

Carbon  dioxide  is  a  colorless,  odorless  gas,  which 
by  cold  and  pressure  may  be  easily  condensed  to  a 
liquid.  When  the  latter  is  allowed  to  escape  from 


94  INORGANIC  CHEMISTRY. 

a  fine  jet  a  part  of  it  evaporates  instantaneously, 
absorbing  enough  heat  from  the  remainder  to  freeze 
it  into  a  white,  crystalline  solid,  like  snow.  The 
temperature  of  this  solid  is  about  —  78°  C.,  and  if 
it  be  pressed  between  the  fingers  it  produces  a  pain- 
ful blister,  and  sensations  like  a  burn. 

Carbon  dioxide  dissolves  to  a  considerable  ex- 
tent in  water,  especially  under  pressure.  Some 
natural  waters,  from  so-called  mineral  springs,  are 
heavily  charged  with  it,  and  effervesce  upon  expos- 
ure to  the  air.  The  Saratoga  and  Seltzer  waters 
are  good  examples.  Soda-water  is  merely  water 
artificially  charged  with  carbon  dioxide ;  and  to  the 
same  gas  champagne  owes  its  sparkle  and  beer  its 
foam.  By  standing  in  the  open  air  these  drinks 
soon  lose  their  gas,  and  become  flat  and  valueless. 

In  the  chemistry  of  cooking,  carbon  dioxide  plays 
an  important  part.  As  evolved  by  yeast  it  makes 
bread  light  and  porous  ;  and  the  same  end  is  at- 
tained less  wholesomely  and  perfectly  by  the  aid 
of  saleratus  and  baking-powders.  All  the  latter 
preparations  owe  their  value  to  the  carbon  diox- 
ide which  they  are  capable  of  developing ;  and  all 
leave  residues  behind  which  render  bread  inferior 
in  quality. 

Like  nitrogen,  carbon  dioxide  is  incapable  of 
sustaining  either  combustion  or  life.  It  is  not  in 
any  sense  poisonous,  like  the  monoxide — it  is  sim- 
ply inert.  We  throw  it  off  from  our  lungs,  and  re- 
place it  with  fresh  oxygen ;  it  is  no  longer  fit  for 
breathing. 

EXPERIMENT  43. — Lower  a  lighted  candle  into 
a  jar  of  carbon  dioxide.  The  flame  will  at  once 
be  extinguished.  Chemical  fire-engines  are  simply 


CARBON. 


95 


machines  which  generate  carbon  dioxide,  and  throw 
it,  mixed  with  water,  upon  fires. 

Carbon  dioxide  sometimes  accumulates  in  old 
wells,  vaults,  and  cisterns,  and  in  the  great  vats  of 
breweries  ;  and  the  workman  who  descends  into 
such  a  place  to  clean  it  out  may  in  consequence  be 
suffocated.  Many  fatal  accidents  of  this  kind  have 
happened  ;  so  that  it  is  always  best,  before  entering 
a  place  where  carbon  dioxide  may  be,  to  lower  into 
it  a  lighted  candle.  If  the  latter  burns,  the  air  is 
fit  to  breathe ;  if  it  goes  out,  then  let  the  place 
be  thoroughly  ventilated.  The  gas  also  collects  at 
times  in  unused  galleries  of  coal-mines,  where  it  is 
known  to  the  miners  as  choke-damp.  In  some  places 
it  issues  in  quantity  from  crevices  in  the  earth,  as  at 
the  Grotto  del  Cane*  in  Italy.  Here  it  forms  a 
layer  on  the  bottom  of  a  small  cave ;  a  man,  enter- 
ing, has  his  head  above  the  level  of  the  gas,  and 
does  not  notice  it;  but  a  dog,  carried  in  by  the 
guide,  when  placed  upon  the  floor,  is  immediately 
overcome. 

The  fact  that  carbon  dioxide  is  about  half  as 
heavy  again  as  air  may  easily  be  illustrated  by  ex- 
periment. 

EXPERIMENT  44. — Slowly  invert  a  jar  of  the  gas 
a  short  distance  above  the  flame  of  a  candle.  The 
latter  will  go  out,  showing  that  carbon  dioxide  de- 
scends. So,  also,  we  may  pour  the  gas  from  one 
vessel  to  another,  almost  as  if  it  were  a  liquid. 

EXPERIMENT  45. — Put  two  glass  jars  in  the  pans 
of  a  pair  of  scales,  and  balance  them  nicely  against 
each  other.  Pour  carbon  dioxide  into  one  of  the 
jars  and  the  latter  will  sink,  having  become  the 

*  Grotto  of  the  Dog. 


96  INORGANIC  CHEMISTRY. 

heavier  (Fig.  27).  The  actual  density  of  the  gas,  re- 
ferred to  hydrogen  as  unity,  is  22 ;  that  of  carbon 
monoxide  is  14. 

In  its  relations  to  the  atmosphere,  and  through 


FIG.  27.  —Weighing  Carbon  Dioxide. 

the  atmosphere  to  life,  carbon  dioxide  is  a  substance 
of  the  greatest  importance.  Were  its  proportions 
to  be  but  moderately  increased,  all  animals  would 
die ;  were  it  wholly  withdrawn,  vegetable  life  would 
perish.  Fortunately,  its  quantity  in  the  atmosphere 
varies  but  little,  in  spite  of  the  fact  that  every  fire 
and  every  breathing  animal  withdraws  oxygen  from 
the  air  and  replaces  it  with  carbon  dioxide.  How 
is  the  balance  preserved  ? 

In  organized  life  we  have  a  steady  circulation 
of  carbon.  Directly  or  indirectly,  all  animals  de- 
pend upon  vegetable  food,  the  carbon  of  which 
becomes  a  part  of  the  animal  tissues.  These  un- 
dergo, through  the  medium  of  the  lungs,  a  sort  of 


CARBON. 


97 


slow  combustion,  whereby  the  animal  heat  is  kept 
up,  and  in  consequence  of  which  the  carbon  is  con- 
verted into  carbon  dioxide  and  thrown  off  into  the 
outer  air.  Now  comes  into  play  one  of  the  most  re- 
markable functions  of  plant-life:  the  plant  which 
furnishes  the  animal  with  food,  in  turn  seizes  upon 
the  carbon  dioxide  which  the  latter  has  rejected, 
and  reconverts  its  carbon  into  vegetable  tissue. 
The  leaf,  in  presence  of  sunlight,  decomposes  car- 
bon dioxide,  retaining  its  carbon  and  setting  the 
oxygen  free.  Without  the  help  of  the  sunbeam 
this  work  could  not  be  done ;  during  the  night  the 
leaves  rest  from  their  labors.  In  the  manner  thus 
briefly  outlined,  the  plant  and  the  animal  balance 
each  other  in  Nature,  and  help  to  keep  even  the 
proportion  of  carbon  dioxide  in  the  air. 

With  nitrogen,  carbon  forms  one  compound — a 
colorless  gas,  having  an  odor  suggestive  of  peach- 
kernels,  and  burning  with  a  beautiful  purple  flame. 
Its  formula  is  C2N2 ;  and  its  name,  cyanogen,  is  de- 
rived from  two  Greek  words  which  indicate  that  it 
forms  some  compounds  which  are  blue.  Prussian 
blue  is  one  of  them.  It  unites  with  metals  just  as  if 
it  were  an  element,  forming  salts  which  are  known 
as  cyanides.  Compounds  which  thus  behave  like  ele- 
ments are  not  infrequent,  and  are  called  compound 
radicles.  In  the  present  case  the  true  compound 
radicle,  however,  is  the  half  of  C2N2,  or  CN,  which 
does  not  exist  in  the  free  state,  but  only  in  cyanides, 
such  as  potassium  cyanide,  KCN,  and  so  on.  Some- 
times the  CN  group  is  represented  by  an  abbre- 
viated symbol,  Cy  ;  and  on  this  plan  free  cyanogen 
would  be  written  Cy2.  Hydrocyanic  acid,  popu- 
larly called  prussic  acid,  has  the  formula  HCN.  It 


98  INORGANIC  CHEMISTRY. 

is  one  of  the  deadliest  poisons.  Cyanogen  and  its 
derivatives  are  best  studied  among  organic  com- 
pounds, since  they  are  commonly  of  organic  origin. 
Their  further  consideration,  therefore,  must  be  de- 
ferred to  the  proper  chapter. 


CHAPTER  XL 

COMBINATION  BY  VOLUME. 

WE  have  already  noticed  the  fact  that  the  num- 
bers 14,  1 6,  35.5,  80,  and  127  represent  not  only  the 
atomic  weights  of  N,  O,  Cl,  Br,  and  I  respectively, 
but  also  the  relative  weights  of  equal  volumes  of 
these  elements,  in  the  condition  of  gas  or  vapor, 
compared  with  hydrogen  as  unity.  In  general,  with 
a  very  few  exceptions  to  be  noted  hereafter,  the 
atomic  weight  of  an  element  expresses  also  its  vapor 
density. 

In  carbon,  however,  we  meet  with  an  element 
which  does  not  readily  vaporize,  so  that  we  can  not 
directly  test  the  accuracy  of  the  foregoing  statement 
with  regard  to  it.  Its  atomic  weight  being  12,  its 
vapor  should  be  just  twelve  times  heavier  than  hy- 
drogen ;  but  whether  it  is  or  not  we  are  unable  to 
experimentally  determine.  We  may,  nevertheless, 
study  some  of  the  gaseous  compounds  of  carbon,  and 
see  whether  they  can  shed  any  light  on  the  subject. 
Or,  in  more  general  terms,  we  may  try  to  discover 
whether  any  simple  relation  connects  the  density  of 
a  compound  gas  with  the  densities  of  the  gaseous 
elements  contained  in  it. 

If  we  refer  back  to  the  chapter  upon  atomic 
weights,  we  shall  see  that  the  elementary  gases  hy- 


100  INORGANIC  CHEMISTRY. 

drogen,  oxygen,  and  nitrogen,  combine  by  volume 
in  very  simple  ratios.  A  few  of  these  may  well  be 
reconsidered  here,  with  the  addition  of  figures  show- 
ing the  volumes  of  the  resulting  compounds  in  the 
state  of  gases  or  vapors : 

2  vols.  H  with  i  vol.  O,  in  all  3  vols.,  form  2  vols.  HaO. 

3  "     H     "     i    "    N,  "  "   4    "        "2     "      NH3. 
2     "     N     "     i    "     O,  "  "    3    "        "2     "      N2O. 

2      "      N      "      3     "      O,  "    "     5      "  "2      "       NaO3. 

In  short,  in  each  of  these  cases,  the  elements 
unite  with  condensation,  and  two  volumes  of  a  com- 
pound result.  So  also  with  nitric  acid,  HNO3,  in 
which  five  volumes  of  H,  N,  and  O  condense  to  two 
volumes  of  the  compound  vapor.  In  hydrochloric 
acid,  HC1,  a  substance  to  be  described  in  a  future 
chapter,  we  have  an  example  of  a  simpler  kind. 
One  volume  of  H  unites  with  one  volume  of  Cl 
without  condensation,  and  here  again  two  volumes  of 
the  compound  gas,  HC1,  are  formed. 

From  these  data,  or  rather  from  the  two-volume 
law  in  general,  we  can  easily  calculate  the  density  of 
any  compound  gas.  For  example,  steam  is  formed 
by  the  union  of  two  unit  volumes  of  hydrogen, 
weighing  two  combining  units,  with  one  volume  of 
oxygen  which  weighs  sixteen.  The  resulting  two 
volumes  of  course  weigh  eighteen  units,  and  one 
volume  weighs  half  as  much,  or  is  nine  times  heavier 
than  hydrogen.  Hence  we  may  say  that  the  density 
of  a  compound  gas  or  vapor,  compared  with  hydrogen  as 
unity,  is  half  its  molecular  weight*  Thus — 

*  To  find  the  density  referred  to  air  as  unity,  divide  the  values 
given  according  to  this  rule,  by  1443.     Why  ? 


COMBINATION* 

HC1.    Mol.  weight,  I  +  35.5  =  36.5.  Density,  18.75. 
HaO.      "          "      2  +  16     =  18.  "         9. 

H3N.      "          "      3  +  14     =  17.  "         8.5, 

N2O.      "  '•    28  +  16     =  44.  "       22. 

N2O3.     "  "    28  +  48     =  76.  "       38. 

HNO3.  "  "      i  +  14  +  48  =  63.  "        31.5. 

We  may  now  apply  this  rule  to  the  carbon  com- 
pounds, assuming  the  density  of  carbon  vapor  to  be 
12,  and  see  whether  the  results  obtained  are  correct : 

CH4.   Mol.  weight,  12  +    4=16.     Density,  8. 
CaH4.      "          "     24+    4  =  28.          "      14. 

CaHa.        "  "       24+     2  =  26.  "         13. 

CO.         "          "     12  +  16  =  28.          "      14. 

COa.          "  "       12  +  32  =  44.  "        22. 

CaNa.        "  "       24+28  =  52.  "         26. 

These  densities  exactly  agree  with  the  results  which 
have  been  reached  by  direct  experiment.  Hence 
we  may  conclude  that  just  as  16  represents  the  den- 
sity of  oxygen,  so  also  12  stands  for  the  density  of 
carbon  in  its  gaseous  compounds  ;  and  the  more  we 
study  the  latter  the  stronger  the  evidence  will  be- 
come. In  a  similar  way  we  can  investigate  the 
volatile  compounds  of  other  non-volatile  elements, 
and  prove  that  the  two-volume  law  above  indicated 
is  of  universal  application.  The  seeming  exceptions 
to  it  will  be  explained  in  another  chapter. 

Among  the  carbon  compounds  cited  above  are 
three  which  deserve  further  consideration  at  this 
point.  Each  of  the  formulae  C2H4,  C2H2,  and  C2N2 
is  capable  of  being  halved,  and  the  simpler  formulae 
CH2,  CH,  and  CN  will  represent  just  as  well  the 
composition  of  these  substances  by  weight.  CH2 
indicates  precisely  the  same  ratio  between  C  and  H 
as  the  more  complex  formula  C2H4;  why,  then, 


102 

should  we  not  by  preference  adopt  it?  Simply  be- 
cause the  density  of  the  gas,  doubled,  gives  us  its 
molecular  weight,  and  the  latter  agrees  only  with 
the  higher  formula.  So  also  with  the  other  cases. 
C2H4  is  one  of  a  series  of  hydrocarbons — C2H4, 
C3H6,  C4H8,  C5H10,  etc. — in  which  the  relative  pro- 
portions of  hydrogen  and  carbon  do  not  vary.  But 
in  vapor  density  these  substances  differ  widely,  and 
from  it,  as  well  as  from  other  evidence  to  be  con- 
sidered under  organic  chemistry,  we  deduce  the 
formulas  given  above.  In  short,  the  same  kinds  of 
atoms  may  combine  in  the  same  relative  proportions 
so  as  to  form  many  different  molecular  groups  or 
compounds  having  different  vapor  density.  If  by 
experiment  we  ascertain  the  latter,  we  are  able  in 
any  given  case  to  assign  a  correct  molecular  weight, 
and  from  that  to  draw  conclusions  as  to  the  proper 
formula. 

Two  of  the  oxides  of  nitrogen  will  illustrate  the 
application  of  these  principles  still  further.  In  a 
previous  chapter  we  gave  them  provisionally  the 
formulae  N2O2  and  N2O4,  so  as  to  bring  out  more 
clearly  the  law  of  multiple  proportions.  Properly, 
however,  these  particular  compounds  should  be  rep- 
resented by  the  formulae  NO  and  NO2  respectively. 
If  the  formula  of  the  first  were  N2O2,  its  density 
would  be  30 ;  whereas  experiment  shows  it  to  be 
only  15.  Accordingly,  we  halve  the  formula,  and  so 
get  at  the  true  molecular  weight.  So  also  with  the 
other  oxide. 

The  more  we  study  the  properties  of  gases,  the 
more  we  shall  be  impressed  with  the  simplicity  of 
the  laws  which  govern  them.  They  expand  equally 
by  heat,  and  are  affected  equally  by  pressure ;  and 


COMBINATION  BY    VOLUME. 


103 


between  the  molecular  weight  and  the  density  we 
have  just  recognized  a  very  close  relation.  All 
these  regularities,  with  others  which  fall  without 
the  scope  of  this  book,  suggest  a  general  law  for 
gases,  and  such  a  law  was  announced  by  the  Italian 
physicist,  Avogadrp,  in  1811.  It  may  be  stated  as 
follows : 

Equal  volumes  of  gases,  compared  under  identical 
conditions  of  temperature  and  pressure,  contain  equal 
numbers  of  molecules. 

This  law  may  be  deduced  both  from  chemical 
and  physical  evidence,  and  has  strong  mathematical 
foundations  ;  accordingly,  it  is  accepted  by  chemists 
and  physicists  alike.  We,  however,  need  to  con- 
sider it  only  in  its  chemical  bearings,  and  in  addi- 
tion to  what  has  already  been  said,  especially  with 
regard  to  the  difference  between  atoms  and  mole- 
cules. " 

So  far,  our  standards  of  comparison  have  been 
the  atom  of  hydrogen  for  atomic  and  molecular 
weights,  and  the  unit  volume  of  hydrogen  for  vol- 
umes. Using  these  standards,  we  have  found  that 
for  all  the  elementary  gases  so  far  studied,  density 
and  atomic  weight  have  both  been  represented  by 
the  same  number ;  which  shows  that  equal  volumes 
of  H,  N,  O,  etc.,  contain  equal  numbers  of  atoms.  For, 
if  an  atom  of  O  is  sixteen  times  heavier  than  an  atom 
of  H,  and  a  litre  of  O  sixteen  times  heavier  than  a 
litre  of  H,  then  the  litre  of  O  arid  the  litre  of  .H  must 
contain  precisely  the  same  number  of  atoms.  With 
compound  gases,  on  the  other  hand,  a  different  re- 
lation holds ;  and,  as  we  have  seen,  the  molecular 
weight  is  not  equal  to,  but  double,  density.  The 
reason  for  this  difference  is,  that  we  have  been  com- 


104  INORGANIC  CHEMISTRY. 

paring  molecules  with  atoms ;  whereas,  in  order 
to  verify  Avogadro's  law,  we  should  compare  mol- 
ecules only  with  each  other. 

If,  now,  we  assume  that  the  molecule  of  hydro- 
gen consists  of  two  atoms,  with  a  molecular  weight 
of  two,  and  represent  in  a  like  manner  the  molecules 
of  the  other  elements  by  OO,  NN,  C12,  Br2,  I2,  etc., 
we  shall  find  that  both  elements  and 'compounds 
will  come  simply  and  regularly  under  Avogadro's 
law.  Then,  for  every  gas  or  vapor,  elementary  or 
compound,  the  density  will  be  one  half  the  molecu- 
lar weight ;  a  ratio  which  is  due  to  the  fact  that  the 
half-molecule,  or  atom  of  hydrogen,  is  taken  as  our 
standard  of  comparison. 

But  the  molecule  of  an  element  is  not  necessarily 
a  double  atom.  The  density  of  ordinary  oxygen,  for 
example,  is  16;  while  that  of  ailotropic  oxygen,  or 
ozone,  is  half  as  heavy  again,  or  24.  We  have  here 
two  different  molecular  groups  formed  by  the  same 
kind  of  atom ;  and  if  the  molecule  of  oxygen  is  O2, 
then  the  molecule  of  ozone  must  be  O3,  with  a  mo- 
lecular weight  of  48.  With  mercury  and  cadmium, 
the  vapor  density  is  half  the  atomic  weight ;  hence 
the  latter  is  identical  with  the  molecular  weight, 
and  the  single  atom  and  the  molecule  are  the  same. 
Phosphorus  and  arsenic,  on  the  other  hand,  form 
vapors  twice  as  heavy  as  their  atomic  weights 
would  indicate,  and  their  molecules  therefore  contain 
four  atoms.  These  points  will  be  considered  more 
fully  when  we  come  to  describe  these  elements.* 

*  Fuller  discussion  of  the  points  brought  forward  in  this  chapter 
may  be  found  in  Cooke's  "Chemical  Philosophy,"  Cooke's  "New 
Chemistry,"  Wurtz's  "  Atomic  Theory,"  or  Remsen's  "  Theoretical 
Chemistry. " 


CHAPTER  XII. 

VALENCY. 

IF  we  examine  the  formulas  of  many  chemical 
compounds,  we  shall  at  first  be  struck  with  the 
great  diversity  of  character  among  them  ;  but,  upon 
a  closer  inspection,  certain  remarkable  regularities, 
of  great  theoretical  importance,  will  appear.  Let 
us  begin  with  some  of  the  compounds  of  hydrogen : 

I.  II.  III.  IV. 

HF.  H2O.  H3N.  H4C* 

HC1.  H2S.  H3P.  H4Si. 

HBr.  H2Se.  H8As. 

HI.  H2Te.  H3Sb. 

Here  we  have  fifteen  elements,  which  unite  with 
hydrogen  in  such  manner  as  to  fall  into  four  well- 
defined  natural  groups.  These  suggest  the  follow- 
ing considerations : 

Every  elementary  atom  has  a  definite  capacity 
for  uniting  with  other  atoms,  which  we  may  call 
its  valency. f  Let  us  again  take  hydrogen  as  our 
standard  of  comparison,  and  assume  its  valency  to 
be  unity.  Then  the  elements  in  the  first  column  of 

*  This  particular  hydrocarbon  is  given  here  because  it  contains  a 
higher  proportion  of  hydrogen  than  any  other. 

f  Also  called  by  various  writers  "  valence,"  "  quantivalence,"  or 
"  atomicity." 


106  INORGANIC  CHEMISTRY. 

the  table,  which  unite  atom  for  atom  with  hydro- 
gen, may  be  called  univalent,  those  which  take  two 
atoms  of  hydrogen  bivalent,  and  those  in  the  third 
and  fourth  columns  trivalent  and  quadrivalent  re- 
spectively. The  atoms  themselves,  with  reference 
to  their  valency,  may  be  concisely  termed  monads, 
dyads,  triads,  and  tetrads — these  names  being  derived 
from  the  Greek  numerals.  Later  on  we  shall  meet 
with  quinquivalent  and  sexivalent  elements,  whose 
atoms  are  called  pentads  and  hexads  respectively. 

The  proportions  in  which  atoms  combine  to- 
gether depend  upon  valency.  Thus,  one  monad 
can  unite  with  one  monad,  one  dyad  with  two 
monads,  one  triad  with  three  monads,  and  one  tet- 
rad with  four  monads.  This  is  shown  in  the  fore- 
going table,  and  also  in  the  following  formulae. 
The  Roman  numerals  serve  to  indicate  the  valency 
of  the  several  elements  : 

K'Cl1.  K'Br1.  Na'F.  AgT. 

CyO".  Ags'O'1.  Naa'Su.  K9!S". 

FW.  As^Cl,1.  SbmBr3'.  Bi111!,1. 

C'CU'.  C'Br*1.  SiiTF41.  SiiTI4l. 

Again,  one  dyad  unites  with  one  dyad,  two  triads 
with  three  dyads,  and  one  tetrad  with  two  dyads, 
thus: 

Cai!Oil.  BauSH.  Zn"O".  Hg"S". 

B2m03ii.  N2ii!03il.  SW'S,11.  BiV'S,11. 

CW.  CITS,U.  Si'W.  SilTS,!l. 

In  each  of  these  cases  the  valencies  of  one  element 
exactly  balance  those  of  the  other.  Some  of  the 
symbols  used  belong  to  metals  which  do  not  com- 
bine with  hydrogen,  but  of  which  the  valency  may 
be  determined  with  reference  to  univalent  chlorine 
or  bivalent  oxygen.  Take,  for  example,  some  of 


VALENCY. 

the  compounds  of  potassium,  calcium,  bismuth,  and 

tin: 

K'Cl1.  Ca"Cla'.  BFCla1.  SnlTCl4l. 

Ka'O".  CauO".  BiaiUO3H.  SnivOau. 

In  many  cases  valency  may  be  made  clearer  to  the 
eye  by  a  different  use  of  symbols.  For  instance, 
carbon  unites  with  hydrogen  and  chlorine  to  form 
the  following  series  of  compounds : 


Cl 
Cl 
Cl 
H 


Cl 
Cl 
Cl 
Cl 


Here  we  have  the  hydrogen-atoms  successively  re- 
placed or  substituted  by  chlorine-atoms,  in  such  a 
way  as  to  show  at  a  glance  the  equivalency  of 
these  elements  and  the  quadrivalency  of  the  carbon. 
Still  another  method  of  representing  valency 
consists  in  attaching  to  the  symbol  of  each  element 
the  necessary  number  of  dashes,  thus : 

H-  O=,  N=,  C i,  etc. ;  or  thus : 

H-,          -O-        -N-          -C-etc. 

i 

From  these  symbols  we  may  derive  a  system  of 
structural  formulae,  as  they  are  called,  of  which  the 
following  are  good  examples : 

Free  hydrogen,  H  -  H,  or  Ha. 
"    oxygen,      O  =  O,  or  Oa. 
"    nitrogen,     N  =  N,  or  Ni. 
Water,  H-O-H.  H  H 

Ammonia,  H  -  N  -  H.         Methane,  H  -  C  -  H. 

i 

H 

Carbon  dioxide,  O  =  C  =  O.         Cyanogen,  N  =  C  -  C  =  N. 
Nitrogen  monoxide,  N  =  N.        Nitrogen  trioxide,  O  =  N  \  ~ 

\(X  0  =  N/°  etc. 


108  INORGANIC  CHEMISTRY. 

In  some  cases  we  encounter  formulas  in  which 
the  conditions  of  valency  are  not  satisfied.  For  in- 
stance, in  nitrogen  dioxide,  NO,  we  have 

-N  =  0, 

and  one  of  the  valencies  or  bonds  of  affinity  of  the 
nitrogen-atom  is  uncombined.  Such  a  compound 
is  called  an  unsaturated  compound,  and  it  enters 
into  further  union  with  other  elements  with  very 
great  ease.  Thus,  from  the  compound  just  cited, 
by  combination  with  chlorine,  we  get  a  substance 
having  the  formula  Cl  —  N=O,  and  in  which  we  see 
a  triad  united  with  a  monad  and  a  dyad  in  such 
a  way  that  the  valencies  exactly  balance.  It  will 
be  seen  at  once  that  the  molecules  of  free  hydro- 
gen, oxygen,  and  nitrogen  are  to  be  regarded  as 
saturated  compounds,  while  the  free  atoms,  if  they 
could  exist  separately,  would  be  unsaturated.  In 
many  chemical  changes  the  elementary  atoms  are 
probably  set  free,  but  immediately  re-enter  into 
union  with  each  other  to  form  molecules. 

In  the  case  of  cyanogen  we  meet  with  a  group 
of  atoms  which  behaves  like  an  element  and  is 
called  a  compound  radicle.  The  formula  of  the 
gas  is  given  above,  and  represents  really  two  CN 
groups  united  to  C2N2.  The  CN  group  itself,  the 
true  compound  radicle,  is  univalent,  thus  : 


and  therefore  is  capable  of  combining  with  elements 
in  much  the  same  way  as  chlorine.     For  example  : 

Chlorine,  Cl  -  Cl.  Cyanogen,  CN  -  CN. 

Hydrochloric  acid,  H  -  Cl.       Hydrocyanic  acid,  N  =  C  -  H. 
Potassium  chloride,  K  -  Cl.     Potassium  cyanide,  K  -  CN,  etc. 


VALENCY. 


109 


Care  must  be  taken  not  to  misapprehend  the 
meaning  of  these  "  structural  "  formulae.  They  are 
not  intended  to  represent  the  relative  position  of 
the  atoms  in  space,  but  merely  to  indicate  to  the 
eye  the  chemical  relations  of  the  substances  thus 
symbolized.  By  their  aid  chemical  reactions  be- 
come more  easily  intelligible,  and  in  many  cases 
they  help  the  chemist  to  predict  the  composition 
and  best  mode  of  preparing  compounds  even  in  ad- 
vance of  actual  discovery.  The  whole  theory  of 
valency  will  become  clearer  when  we  study  it  in 
the  light  of  organic  chemistry  ;  and  one  more  illus- 
tration of  it  will  suffice  for  the  present  chapter. 

A  brief  reference  was  made  in  a  previous  chap- 
ter to  three  important  classes  of  compounds,  acids, 
bases,  and  salts.  So  far  we  have  studied  but  two 
important  acids  —  namely,  nitric  acid,  HNO3,  and 
carbonic  acid,  H2CO3.  These  have  the  following 
structural  formulae  : 


In  these  formulae  we  may  regard  the  NO3  group 
of  atoms,  which  is  found  in  all  nitrates,  as  univa- 
lent  ;  while  the  CO3  group,  which  characterizes  the 
carbonates,  is  bivalent,  as  the  two  hydrogen-atoms 
united  with  it  clearly  show.  Now,  the  salts  of  these 
acids  are  really  formed  by  replacing  the  hydrogen 
by  metals  ;  and  just  here  the  laws  of  valency  come 
into  play.  Thus,  with  univalent  metals,  nitrates  are 
formed  having  formulae  like  the  subjoined  : 

H-NO3.        K-NO3.        Na-NO3.        Ag-NO». 
With  bivalent  metals  we  get  salts  like  these  : 


HO  INORGANIC  CHEMISTRY. 

Pb(N03)2,  or  Pb  <  ££.  Ca(N03)2,  or  Ca  (  ££  j. 

And  with  a  trivalent  metal,  like  bismuth,  we  get  — 


Bi(NO3)3,  orBi-NO3  or  BiN3O9. 

XNO3, 

Since  these  salts  are  called  respectively  potassium, 
sodium,  silver,  lead,  calcium,  and  bismuth  nitrates, 
it  is  plain  that  the  acid  itself  might  fairly  be  named 
hydrogen  nitrate.  That  is,  in  acids,  hydrogen, 
which  is  an  essential  constituent  of  every  acid,  be- 
haves chemically  like  a  metal,  and  gives  us  an  addi- 
tional argument  in  favor  of  its  metallic  character. 
These  formulas  also  show  us  that  the  nitrate  of  any 
metal  may  be  represented  as  resulting  from  the 
combination  of  univalent  NO3  with  the  metal  in  a 
proportion  depending  upon  the  valency  of  the  lat- 
ter. Hence,  if  we  know  the  valency  of  a  metal,  we 
can  at  once  write  the  formula  of  its  nitrate. 

With  carbonic  acid  similar  rules  hold  good  ; 
only  the  hydrogen  may  be  either  partly  or  wholly 
replaced.  Thus,  we  have  : 

HaC03.        KHCOs.        K2C03.        NaHCO3.        Na3CO3. 
PbCO3,  CaCO3,  etc. 

As  we  become  acquainted  with  more  acids,  we 
shall  find  like  principles  always  to  be  applicable  ; 
and  that  a  knowledge  of  valency  will  enable  us  to 
write  a  vast  number  of  formulas  which  could  not 
possibly  be  remembered  unless  connected  by  some 
such  general  law. 


CHAPTER  XIII. 

THE   CHLORINE   GROUP. 

THE  four  univalent  elements,  fluorine,  chlorine, 
bromine,  and  iodine,  are  so  similar  in  their  chemi- 
cal relations  that  they  form  an  exceedingly  definite 
natural  group.  In  their  differences  they  exhibit  a 
remarkable  gradation  of  properties,  which  follows 
the  order  of  their  atomic  weights.  In  the  free  state 
fluorine  is  unknown,  but  chlorine  is  a  greenish-yel- 
low gas,  brpmine  is  a  heavy,  brownish-red  liquid, 
and  iodine  is  a  black  solid  which  forms  beautiful 
purple  vapors.  With  hydrogen,  fluorine  unites  so 
strongly  that  the  two  elements  can  not  be  directly 
separated  from  each  other ;  chlorine  combines  vig- 
orously, bromine  easily,  and  iodine  only  with  diffi- 
culty. In  general,  chlorine  acts  more  energetically 
upon  other  substances  than  bromine,  while  iodine  is 
the  least  active  of  all.  As  a  rule,  the  compounds 
of  bromine  have  properties  intermediate  between 
those  of  chlorine  and  iodine.  These  three  elements 
also  resemble  each  other  in  odor. 

FLUORINE  is  found  in  nature  in  various  min- 
erals, and  minute  quantities  of  its  compounds  also 
occur  in  bones,  milk,  and  blood.  Its  atomic  weight 
is  19,  and  its  chief  sources  are  the  two  minerals  fluor- 
spar and  cryolite.  The  latter,  which  is  brought  in 
6 


112  INORGANIC  CHEMISTRY. 

great  quantities  from  Greenland,  is  a  fluoride  of 
aluminum  and  sodium,  3NaF,AlFs ;  and  is  used  in 
making  soda,  alum,  and  porcelain  glass.  Just  as 
the  compounds  of  oxygen  with  other  elements  are 
called  oxides,  the  compounds  of  fluorine  are  termed 
fluorides.  So,  also,  we  have  chlorides,  bromides, 
and  iodides,  formed  by  chlorine,  bromine,  and  iodine 
respectively.  With  hydrogen  these  elements  form 
acids,  as  follow  : 

Hydrogen  fluoride,  or  hydrofluoric  acid,  HF. 
"  chloride,  "  hydrochloric  "  HC1. 
"  bromide, "  hydrobromic  "  HBr. 
"  iodide,  "  hydriodic  "  HI. 

So  far,  all  attempts  to  isolate  fluorine  have  been 
unsuccessful.  Its  chemical  activity  seems  to  be  so 
great  that  the  moment  it  is  set  free  it  combines  at 
once  with  whatever  substances  may  happen  to  be 
near  it.  It  is  also  the  only  element  which  has  not 
yet  been  made  to  combine  with  oxygen. 

The  only  fluorine  compound  sufficiently  impor- 
tant for  description  here  is  hydrofluoric  acid.  This 
is  usually  prepared  by  treating  calcium  fluoride, 
CaF2,  commonly  known  as  fluor-spar,  with  sulphu- 
ric acid.  Any  other  metallic  fluoride  would  do, 
but  this  one  is  the  most  abundant.  The  reaction  is 
as  follows : 

CaF2  +  H2SO4  =  CaSO4  +  2HF. 

The  pure  acid  is  a  very  volatile  liquid,  having 
the  most  violently  corrosive  properties.  A  drop  of 
it  on  the  skin  will  produce  a  painful  ulcer  which 
may  not  heal  for  several  weeks.  Even  the  weaker 
acid  containing  water,  such  as  is  commonly  pre- 
pared, has  to  be  handled  with  extreme  care. 


THE  CHLORINE  GROUP.  113 

Hydrofluoric  acid  is  chiefly  remarkable  for  its 
power  of  attacking  glass,  which  may  be  shown  by 
the  following  experiment : 

EXPERIMENT  46. — Cover  a  sheet  of  glass  with 
wax,  and  cut  a  design  through  the  wax  with  the 
point  of  a  needle.  Make  a  small  dish  or  tray  out 
of  a  piece  of.  sheet-lead,  and  in  it  mix  some  pow- 
dered fluor-spar  to  a  paste  with  strong  sulphuric 
acid.  Place  the  prepared  glass  over  this  dish,  face 
downward,  and  warm  gently.  Wherever  the  wax 
has  been  scratched  away,  the  glass  will  be  corroded. 

This  process  is  practically  used  for  etching  de- 
signs upon  glass,  for  marking  the  graduation  upon 
the  stems  of  thermometers,  and  so  on.  The  com- 
mercial acid  contains  much  water,  and  is  preserved 
in  bottles  made  of  gutta-percha. 

CHLORINE,  the  atomic  weight  of  which  is  35.5, 
is  by  far  the  most  important  element  of  this  group. 
It  is  found  in  nature  in  many  compounds,  the  most 
abundant  one  being  sodium  chloride,  NaCl,  or  com- 
mon salt.  This  is  the  chemist's  starting-point  for 
the  preparation  of  chlorine  and  of  all  its  other  com- 
pounds. 

EXPERIMENT  47. — In  a  large  flask  provided  with 
a  delivery-tube  mix  one  part  of  common  salt,  one  of 
manganese  dioxide,  two  of  sulphuric  acid,  and  two 
of  water.  Upon  heating  gently,  chlorine  gas  will  be 
evolved  in  a  continuous  stream,  and  may  be  col- 
lected by  displacement  (Fig.  28).  It  can  not  conve- 
niently be  collected  over  water  or  mercury,  since  it 
is  quite  soluble  in  the  one  and  it  corrodes  the  other. 

In  this  experiment  two  different  reactions  take 
place.  First,  the  sulphuric  acid  attacks  the  sodium 
chloride,  forming  sodium  sulphate  and  setting  hy- 


INORGANIC  CHEMISTRY. 


drochloric  acid  free.    The  latter  then  reacts  upon 
the  manganese  dioxide,  giving  up  its  hydrogen  to 


FIG.  28. — Preparation  of  Chlorine. 

unite  with  the  oxygen  of  the  latter,  and  so  liberat- 
ing the  chlorine.     The  whole  change  is  as  follows : 

2NaCl  +  2  H2SO4  +  MnOa  =  C12  +  NaaSO4  +  MnSO4  +  2HaO. 

A  simpler  but  no  better  mode  of  preparation,  in- 
volving the  same  apparatus,  consists  in  treating  the 
manganese  dioxide  directly  with  common  hydro- 
chloric acid.  The  reaction  then  is— 

MnO3  +  4  HC1  =  MnCla  +  Cla  +  2  H2O. 

In  either  equation  we  have  two  atoms — that  is,  one 
molecule — of  chlorine  set  free.     There  are  still  other 


THE  CHLORINE  GROUP.  n$ 

processes  for  the  manufacture  of  chlorine  which  are 
used  on  a  large  commercial  scale,  but  they  need  no 
extended  notice  here.* 

Chlorine  was  discovered  by  Scheele  in  1774. 
It  is  a  greenish-yellow  gas,  two  and  a  half  times 
heavier  than  air,  and  having  a  highly  irritating 
odor.  Even  a  trace  of  it,  if  inhaled,  will  produce  a 
painful  sense  of  suffocation.  By  cold  and  pressure 
it  may  be  condensed  to  a  heavy  yellow  liquid,  but 
it  has  not  yet  been  solidified. 

Cold  water  absorbs  about  two  and  a  half  times 
its  bulk  of  chlorine.  The  solution,  which  is  known 
in  the  laboratory  as  chlorine-water,  is  yellowish,  and 
smells  strongly  of  the  gas.  It  is  a  useful  substance 
in  some  of  the  processes  of  chemical  analysis,  but  it 
must  be  kept  in  the  dark,  or  in  a  bottle  covered 
with  black  paper.  Exposed  to  the  light,  chlorine 
decomposes  water,  withdrawing  hydrogen  to  form 
hydrochloric  acid,  and  setting  oxygen  free. 

EXPERIMENT  48. — Fill  a  small  flask  full  of  chlo- 
rine-water, prepared  by  passing  chlorine  into  water 
as  long  as  it  dissolves,  and  invert  it  in  a  dish  of  the 
same  solution.  Leave  the  liquid  for  some  time  ex- 
posed to  sunlight.  Bubbles  of  oxygen  will  form, 
and  collect  in  the  upper  part  of  the  flask  (Fig.  29), 
where  they  may  easily  be  identified. 

Chlorine  unites  vigorously  with  nearly  all  the 
elements,  and  especially  with  the  metals.  A  bit  of 
phosphorus,  plunged  into  a  jar  of  the  gas,  will  spon- 
taneously inflame ;  and  powdered  antimony  or  thin 
copper-foil  will  also  ignite  readily. 

EXPERIMENT    49. — Prepare    some    chlorine    by 

*  A  good  outline  of  these  processes  is  given  in  Wagner's  "  Chemi- 
cal Technology." 


Il6  INORGANIC  CHEMISTRY. 

either  of  the  methods  previously  described,  and  dry 
it  by  allowing  it  to  pass  through  a  tube  containing 


FIG.  29. — Formation  of  Oxygen  from  Chlorine-water. 

lumps  of  calcium  chloride.  Into  a  jar  of  this  per- 
fectly dry  gas  throw  some  powdered  antimony. 
The  latter  will  burn  brilliantly,  filling  the  jar  with 
dense  fumes.  Dip  into  another  portion  of  the 
chlorine  a  piece  of  paper  moistened  with  warm 
turpentine.  This  also  will  ignite  and  burn  with 
a  sooty  flame.  Into  a  third  jar  of  the  gas  plunge 
a  lighted  candle.  It  will  continue  to  burn  with  a 
reddish  flame,  emitting  dense  clouds  of  smoke. 
Combustion,  then,  although  commonly  due  to  ox- 


THE  CHLORINE  GROUP. 


117 


idation,  is  not  always  so.  It  is  simply  a  phenom- 
enon of  violent  chemical  action,  and  may  be  pro- 
duced by  union  either  with  oxygen  or  other  ele- 
ments. 

Although  chlorine  has  a  considerable  number  of 
uses  in  the  arts,  its  chief  practical  importance  is  due 
to  its  property  of  bleaching  vegetable  colors.  This 
is  easily  illustrated : 

EXPERIMENT  50. — Dip  some  slips  of  litmus-paper, 
some  bits  of  bright  calico,  and  some  highly-colored 
flowers  into  chlorine-water.  They  will  be  bleached. 
Add  chlorine-water  to  a  solution  of  indigo,  and  the 
latter  will  be  decolorized.  Characters  written  in 
ordinary  ink  may  be  obliterated  by  exposure  to 
chlorine;  but  printer's  ink,  which  consists  of  car- 
bon, is  not  affected. 

Chlorine  is  also  a  vigorous  disinfectant.  This 
property,  and  its  value  as  a  bleaching  agent,  both 
depend  upon  its  strong  affinity  for  hydrogen,  which 
is  partly  illustrated  in  Experiment  48.  The  igni- 
tion of  turpentine  and  the  burning  of  a  candle  in 
chlorine  are  also  due  to  the  active  union  of  this 
element  with  the  hydrogen  which  they  contain.  In 
most  cases  chlorine  is  applied  for  bleaching  or  dis- 
infecting purposes  in  presence  of  moisture.  The 
latter  gives  up  its  hydrogen,  and  the  oxygen  thus 
set  free  acts  with  especial  vigor,  at  the  moment  of 
its  liberation,  upon  the  coloring-matter  or  putres- 
cent  substance  which  is  to  be  destroyed.  Chlorine, 
therefore,  may  be  regarded  as  indirectly  an  oxidiz- 
ing agent ;  although  in  some  cases  it  acts  destruc- 
tively upon  obnoxious  compounds  by  withdraw- 
ing hydrogen  and  so  breaking  up  their  molecules. 
These  uses  of  chlorine  will  be  considered  further 


Il8  INORGANIC  CHEMISTRY. 

on,  when  we  study  the  properties  of  bleaching- 
powder. 

With  hydrogen,  chlorine  forms  but  a  single 
compound,  hydrochloric  acid,  HC1;  and  some  of 
the  circumstances  under  which  it  is  produced  have 
been  already  described. 

When  equal  volumes  of  hydrogen  and  chlorine 
are  mixed  together  in  the  dark,  they  will  remain 
without  action  upon  each  other  for  an  indefinitely 
long  time.  If  the  jar  or  bottle  containing  them  be 
exposed  to  ordinary  diffused  daylight,  they  will 
slowly  and  quietly  combine ;  but  if  they  are  sud- 
denly brought  from  darkness  into  the  full  glare  of 
the  sun,  they  will  unite  instantaneously  with  ex- 
plosive violence.  This  may  be  experimentally  veri- 
fied by  filling  a  flask  in  the  dark  with  the  gaseous 
mixture,  wrapping  it  in  a  cloth,  and  then  in  strong 
sunlight  pulling  away  the  cloth  by  means  of  a  long 
string.  The  flask  will  be  shattered  by  the  explo- 
sion which  ensues.  Light  is  frequently  instrument- 
al in  bringing  about  chemical  changes.  In  this 
case  it  produces  chemical  union ;  on  the  photo- 
graphic plate  it  causes  decomposition  ;  and  the  fad- 
ing of  colored  fabrics  in  sunlight  also  illustrates  the 
same  thing.  Some  of  these  matters  will  be  further 
discussed  in  other  connections. 

EXPERIMENT  51. — An  additional  example  of  the 
direct  union  of  hydrogen  and  chlorine  is  furnished 
by  the  combustion  of  the  former  "gas  in  the  latter. 
The  apparatus  may  be  arranged  as  in  Fig.  30,  hy- 
drogen being  generated  in  the  flask  in  the  usual 
way,  while  the  jet  dips  into  a  cylinder  or  jar  con- 
taining the  chlorine.  The  hydrogen-flame  should 
be  first  kindled  in  the  air,  with  the  ordinary  precau- 


THE  CHLORINE  GROUP. 


119 


tions  (see  Experiment  7),  and  then  lowered  into  the 
chlorine. 

For  practical   purposes,  however,  hydrochloric 
acid  is  prepared  by  a  wholly  different  method. 


FIG.  30. — Combustion  of  H  in  Cl. 

EXPERIMENT  52.— In  a  glass  flask  provided  with 
a  delivery-tube  heat  some  perfectly  dry  common 
salt  with  about  twice  its  weight  of  strong  sulphuric 
acid.  Hydrochloric  acid  will  be  evolved  with  much 
effervescence,  and  may  be  collected  over  mercury. 
If  an  aqueous  solution  of  the  gas  is  wanted,  the  de- 
livery-tube may  dip  into  a  jar  of  water.  As  the 
experiment  is  conducted  in  the  school-room,  the  re- 
action is  as  follows  : 

NaCl  +  H2SO4  =  NaHSO4  +  HC1. 

In  making  the  acid  on  a  commercial  scale,  a  higher 
temperature  is  applied,  and  only  half  as  much  sul- 
phuric acid  is  taken.  The  reaction  then  is : 

2NaCl  +  HaSO4  =  Na.,SO4  +  2HC1. 


120  INORGANIC  CHEMISTRY. 

When  we  study  sulphuric  acid  and  the  sulphates, 
the  full  significance  of  these  equations  will  ap- 
pear. 

Hydrochloric  acid  is  a  colorless  gas  of  pungent 
odor,  and  density  18.75.  In  it  the  two  component 
gases  are  united  without  condensation.  It  dis- 
solves very  freely  in  water,  and  the  commercial 
hydrochloric  or  muriatic  acid  is  merely  its  strong 
aqueous  solution.  This  solution  emits  acrid,  suf- 
focating fumes,  and  should  be  as  colorless  as 
water;  the  common  acid,  however,  is  bright  yel- 
low, in  consequence  of  impurities.  It  contains 
from  thirty  to  forty  per  cent  of  the  gaseous 
acid. 

Hydrochloric  acid  is  one  of  the  strongest  and 
most  important  of  acids.  It  is  used  extensively  in 
the  manufacture  of  chlorine,  and  for  a  great  variety 
of  other  purposes.  It  dissolves  many  of  the  metals, 
such  as  tin,  zinc,  and  iron — hydrogen  being  evolved, 
and  the  chlorides  of  the  metals  being  formed  : 

Zn  +  2HC1  =  ZnCl2  +  H2. 
Fe  +  2HC1  =  FeCl2  +  H3. 

In  these  reactions  the  metals  replace  the  hydrogen 
of  the  acid,  just  as  in  the  cases  previously  noticed ; 
only  the  salts  formed  are  chlorides.  In  a  similar 
way  hydrofluoric  acid  yields  fluorides,  hydrobromic 
acid  yields  bromides,  and  hydriodic  acid  yields 
iodides.  The  student  may  advantageously  test  the 
solvent  properties  of  hydrochloric  acid  upon  sev- 
eral of  the  commoner  metals.  Some  will  be  dis- 
solved, and  others  not  attacked  at  all;  and  the  solu- 
tions of  the  former  may  be  made  by  evaporation  to 
deposit  crystals  of  chlorides. 


THE  CHLORINE  GROUP. 


Hydrochloric  *  and  nitric  acids  mutually  decom- 
pose each  other,  with  evolution  of  chlorine  : 

HNO3  +  3HC1  =  2H2O  +  NOC1  +  Cla. 

The  compound  NOC1  was  referred  to  in  a  previous 
chapter.  It  is  an  orange-colored  gas  of  slight  im- 
portance. The  mixture  of  acids  is,  however,  very 
important  ;  since,  by  virtue  of  the  chlorine  which  it 
liberates,  it  has  the  power  of  dissolving  gold.  No 
single  acid  will  do  this  ;  and  so  the  alchemists  gave 
the  mixture  the  name  of  aqua  regia,  or  royal  water, 
gold  being  considered  the  king  of  metals.  It  also 
dissolves  platinum. 

EXPERIMENT  53.  —  In  each  of  two  test-tubes  put 
a  bit  of  gold-leaf.  Cover  one  with  nitric  and  the 
other  with  hydrochloric  acid.  Neither  will  be  at- 
tacked. Mix  the  contents  of  both  test-tubes,  and 
warm  gently.  The  gold  will  dissolve,  forming  a 
yellow  solution. 

*  When  hydrochloric  acid  is  spoken  of,  the  aqueous  solution  is 
usually  meant.  The  pure  HC1  is  commonly  specified  as  hydrochloric 
acid  gas. 


CHAPTER   XIV. 

THE  CHLORINE  GROUP — (continued). 

WITH  oxygen  chlorine  does  not  combine  direct- 
ly;  but,  by  indirect  processes,  three  oxides,  C12O, 
C12O3,  and  C12O4,  have  been  obtained.  They  are  all 
gases  of  irritating  odor  and  dangerously  explosive 
character.  With  hydrogen  and  oxygen  chlorine 
yields  a  remarkable  series  of  acids,  of  which  hydro- 
chloric acid  may  fairly  be  considered  the  first  mem- 
ber: 

HC1,         Hydrochloric  acid. 

HC1O,      Hypochlorous   " 

HC1O3,     Chlorous 

HC1OS,     Chloric 

HC1O4,     Perchloric 

It  will  be  observed  that  chlorous  and  chloric  acids 
resemble  in  formula  nitrous  and  nitric  acids,  HNO2 
and  HNO3.  The  prefix  hypo,  which  we  meet  in 
^j/^chlorous  acid,  is  often  used  to  indicate  com- 
pounds which  are  relatively  low  in  a  series.  For 
example,  ^//^sulphurous  and  /^/^phosphorous  acids 
contain  less  oxygen  than  sulphurous  and  phosphor- 
ous acids  respectively.  The  prefix/^/-,  on  the  other 
hand,  as  in  perchloric  acid,  is  expressive  of  higher 
combination.  Thus  we  have  the  terms  /m)xide, 
/^chloride,  etc.,  applied  to  compounds  more  than 


THE  CHLORINE  GROUP.  12$ 

ordinarily  rich  in  oxygen  or  chlorine.  These  names 
are  somewhat  arbitrary,  and  no  definite  rule  gov- 
erns them  without  exception. 

Hypochlorous  acid,  HC1O,  although  unimpor- 
tant by  itself,  forms  some  salts  of  the  very  highest 
importance.  When  chlorine  gas  is  passed  into  a 
cold  and  dilute  solution  of  caustic  soda,  it  is  copi- 
ously absorbed,  and  a  mixture  of  sodium  chloride 
and  sodium  hypochlorite,  NaCIO,  is  produced.  The 
latter  compound  has  a  peculiar,  sickish  odor,  and  is 
used  for  disinfecting  purposes.  It  forms  the  "  La- 
barraque's  solution  "  of  the  drug-stores.  If  chlorine 
be  passed  over  slaked  lime,  instead  of  into  caustic 
soda,  a  mixture  of  calcium  chloride  and  calcium 
hypochlorite  results  from  the  action,  and  this  is  the 
well-known  "  chloride  of  lime,"  or  bleaching-powder 
of  commerce.  The  reaction  which  forms  it  is  as 
follows : 

2CaH2Oa  +  2Cla  =  2H2O  +  CaCU  +  CaCl2O2. 

The  last  symbol  in  this  equation  may  be  written 

O— Cl 
Ca^Q_pi  ;  and,  when  contrasted  with  H-O-C1  and 

Na-O-Cl,  it  serves  to  illustrate  the  bivalency  of  cal- 
cium. 

Bleaching-powder  is  extensively  used  both  for 
bleaching  and  as  a  disinfectant.  It  has  the  peculiar 
odor  which  is  characteristic  of  all  hypochlorites, 
and  it  owes  its  efficiency  in  great  measure  to  the 
readiness  with  which  it  gives  up  its  chlorine.  In 
short,  it  affords  us  a  convenient  means  of  storing 
and  transporting  chlorine  in  an  available  form  for 
most  of  its  practical  applications.  At  the  beginning 
of  this  century  all  linen  and  cotton  fabrics  were 
bleached  by  long  exposure  on  the  grass  to  the  ac- 


124  INORGANIC  CHEMISTRY. 

tion  of  sunlight  and  moisture.  To-day  they  are 
bleached  by  chlorine,  applied  as  a  solution  of  cal- 
cium hypochlorite ;  and  in  a  few  hours,  in  a  small 
area,  more  bleaching  can  be  done  than  was  formerly 
accomplished  in  several  months  on  many  acres  of 
grass-land. 

EXPERIMENT  54.— Shake  up  a  quantity  of  "  chlo- 
ride of  lime  "  with  about  four  times  its  bulk  of  water ; 
allow  the  mixture  to  settle  thoroughly,  and  then 
carefully  pour  off  the  clear  solution.  With  this  so- 
lution repeat  the  bleaching  experiments  given  under 
the  heading  of  Experiment  50.  In  each  case,,  how- 
ever, first  moisten  the  object  to  be  bleached  with 
very  dilute  sulphuric  acid  or  with  vinegar.  Acids 
serve  to  liberate  chlorine  from  bleaching-powder. 

Chlorous  acid  and  the  chlorites  are  wholly  un- 
important; but  in  chloric  acid  and  its  salts  we  meet 
with  compounds  of  considerable  utility  and  interest. 

EXPERIMENT  55. — Pass  a  stream  of  chlorine  gas 
into  a  weak  and  cold  solution  of  caustic  potash.  Po- 
tassium hypochlorite,  K-O-C1,  will  be  formed,  and 
may  be  recognized  by  its  odor  and  bleaching  prop- 
erties. Now  repeat  the  experiment  with  a  hot  and 
strong  solution  of  the  caustic  potash.  Potassium 
chlorate  will  be  produced,  and  will  be  deposited  in 
tabular  crystals  when  the  solution  cools : 

6KOH  +  3C12  =  KC1O3  +  5KC1  +  3H2O. 

Chloric  acid  itself  has  never  been  prepared  quite 
free  from  water.  In  its  most  concentrated  state  it 
is  a  colorless,  sirupy,  intensely  sour  liquid,  resem- 
bling nitric  acid  in  many  of  its  properties.  It  is  so 
powerful  an  oxidizing  agent  that  when  it  is  merely 
dropped  upon  paper  the  latter  will  ignite. 


THE  CHLORINE  GROUP. 


125 


The  chlorates  of  potassium  and  sodium,  KC1O3 
and  NaClO3,  are  compounds  of  commercial  impor- 
tance. Potassium  chlorate  is  especially  useful  as  a 
source  of  oxygen  in  the  manufacture  of  certain  ex- 
plosive mixtures,  and  as  a  medicinal  agent.  It  is 
one  of  the  favorite  remedies  for  sore-throat.  We 
have  already  met  with  it  in  Experiments  4  and  n, 
but  the  following  experiments  may  also  be  profitably 
tried  : 

EXPERIMENT  56. — Allow  a  drop  of  strong  sul- 
phuric acid  to  fall  upon  a  crystal  of  potassium 
chlorate.  There  will  be  violent  action,  and  an  ev- 
olution of  yellow,  pungent  fumes.  The  latter  con- 
sist of  chlorine  tetroxide,  C12O4.  If  too  much 
chlorate  be  used,  an  explosion  may  ensue ;  and  if, 
as  in  Experiment  4,  the  salt  be  mixed  with  sugar  or 
starch,  the  mass  will  take  fire  and  burn  brilliantly. 
A  mixture  of  potassium  chlorate  with  sugar  forms 
a  white  gunpowder  which,  however,  is  too  dan- 
gerous for  practical  use. 

EXPERIMENT  57. — Put  a  bit  of  phosphorus  as 
large  as  a  pea  at  the  bottom  of  a  conical  glass  filled 
with  water.  A  test-tube  will  answer,  but  is  not 
quite  so  convenient.  Throw  in  a  few  crystals  of  po- 
tassium chlorate,  enough  to  cover  the  phosphorus, 
and  then  pour  in  a  little  strong  sulphuric  acid 
through  a  thistle-tube  (Fig.  31).  The  phosphorus 
will  presently  catch  fire,  and  burn  vividly  under 
water.  The  oxygen  necessary  for  its  combustion 
is,  of  course,  supplied  by  the  potassium  chlorate. 
This  experiment  illustrates  the  ease  with  which  chlo- 
rates give  up  their  oxygen. 

EXPERIMENT  58. — Rub  vigorously  together,  in 
a  porcelain  or  iron  mortar,  a  pinch  of  potassium 


126 


INORGANIC  CHEMISTRY. 


chlorate  and  a  pinch  of  sulphur.  Explosions  more 
or  less  sharp  will  result  from  the  friction.  If  a  little 

of  the  mixture  be  placed 
on  an  anvil,  or  upon  an 
iron  plate,  and  struck 
with  a  hammer,  the  ex- 
plosion will  be  almost 
deafening.  Care,  there- 
fore, should  be  taken  not 
to  pulverize  chlorates 
with  other  substances, 
although  by  themselves 
they  may  be  rubbed  to 
powder  with  safety.  In 
this  experiment  we  see 
that  mechanical  energy 
may  produce  a  vigorous 
chemical  action.  All 
these  experiments  illus- 
trate the  peculiarities  of 
chlorates  in  general,  and 
not  merely  those  of  the  potassium  salt  in  particular. 
We  have  already  learned  that  the  most  conven- 
ient mode  of  preparing  oxygen  is  to  heat  potassium 
chlorate;  the  reaction  being  commonly  written: 

KC103  =  KC1  +  O,. 

In  reality,  the  reaction  is  much  more  complicated, 
and  consists  of  two  stages :  First,  part  of  the  chlo- 
rate is  decomposed  by  the  heat,  a  portion  of  its  oxy- 
gen being  liberated,  while  the  remainder  goes  to 
effect  a  further  oxidation  of  some  of  the  original 
salt.  The  equation  is  as  follows: 


FIG.  31. — Combustion  of  Phos- 
phorus under  Water. 


2KC1OS  =  KC1O*  +  KC1  +  O2. 


THE  CHLORINE  GROUP.  127 

In   the   second    stage   the   KC1O4  is   decomposed, 

thus : 

KC1O4  =  KC1  +  2Oa. 

The  compound  KC1O4  is  potassium  perchlorate; 
and  from  it,  by  proper  means,  perchloric  acid, 
HC1O4,  may  be  obtained  as  an  oily  liquid  of  spe- 
cific gravity  1.782.  Thrown  upon  paper  or  wood, 
the  pure  acid  causes  their  immediate  ignition ; 
dropped  upon  charcoal,  it  explodes  with  terrific  vio- 
lence ;  in  contact  with  the  skin,  it  produces  wounds 
which  do  not  heal  for  months. 

There  is  but  one  compound  of  chlorine  with 
nitrogen,  the  formula  being  probably  NC13.  It  is 
an  oily  liquid  of  such  terribly  explosive  properties 
that  it  should  never  be  prepared  except  by  expe- 
rienced chemists,  and  then  only  in  very  small  quan- 
tities. It  was  discovered  by  Dulong,  who  lost  an  eye 
and  three  fingers  in  consequence  of  his  discovery. 

There  are  several  compounds  of  carbon  with 
chlorine ;  but  as  they  are  derivatives  of  hydrocar- 
bons, they  are  usually  described  under  the  head  of 
organic  chemistry.  A  few  formulas  will  suffice  for 
present  examples : 

CH4    yields    CC14. 
C2H4      «        C2C14. 
C3H8       "        C3C18. 

CeHe         "  Cede. 

BROMINE,  the  third  member  of  the  chlorine 
group,  is  the  only  element  known,  except  mercury, 
which  is  liquid  at  ordinary  temperatures.  It  owes 
its  name  to  a  Greek  word  signifying  a  stench,  be- 
cause of  its  terribly  suffocating  odor.  Its  atomic 
weight  is  80,  its  specific  gravity  in  the  liquid  state 


128  INORGANIC  CHEMISTRY. 

is  3.187,  and  it  boils  at  63°  centigrade.  Its  color 
is  dark  red,  almost  black ;  and  it  emits  red  fumes 
which  somewhat  resemble  nitrogen  tetroxide.  It 
has  some  uses  in  analytical  chemistry,  and  it  is  also 
employed  in  the  manufacture  of  certain  organic 
dyes.  Some  of  the  bromides,  especially  potassium 
bromide,  are  important  medicinal  agents ;  and  they 
are  also  considerably  used  in  the  art  of  photog- 
raphy. 

Bromine  is  chiefly  found,  as  sodium  or  magne- 
sium bromide,  in  sea-water  and  the  waters  of  many 
mineral  springs.  At  present  it  is  produced  in  large 
quantities  from  some  salt-wells  in  the  Kanawha  Val- 
ley of  West  Virginia.  After  the  common  salt  has 
crystallized  out  from  the  brine,  the  remaining 
"  mother  liquor  "  is  heated  with  manganese  dioxide 
and  sulphuric  acid.  These  reagents  liberate  bro- 
mine in  precisely  the  same  way  that  they  liberate 
chlorine ;  and  the  bromine  is  distilled  off  into  a  well- 
cooled  receiver. 

The  compounds  of  bromine  are  strikingly  simi- 
lar to  the  compounds  of  chlorine,  but  are  not  quite 
so  numerous.  No  oxide  of  bromine  is  known,  but 

we  have : 

HBrOs,  Bromic  acid, 

HBr,  Hydrobromic  acid, 

NBr3,  Nitrogen  bromide, 

CBr4,  Carbon  tetrabromide,  etc. 

Salts  are  also  known  corresponding  to  hypobro- 
mous  acid,  HBrO  (a  bleaching  acid),  and  perbro- 
mic  acid,  HBrO4. 

IODINE  is  found  in  minute  quantities  in  sea- 
water,  from  which,  in  the  form  of  iodides,  it  is 
taken  up  by  marine  plants.  It  is  obtained,  commer- 


THE  CHLORINE  GROUP.  129 

cially,  from  the  ashes  of  sea- weeds,  which  are  first 
treated  with  water.  The  solution  thus  obtained  is 
then  heated  with  manganese  dioxide  and  sulphuric 
acid,  and  the  iodine  is  thus  set  free.  The  reaction 
is  precisely  like  that  by  which  chlorine  and  bromine 
are  prepared. 

The  element  itself  is  a  black  solid  with  a  metal- 
lic luster,  and  an  odor  faintly  resembling  that  of 
chlorine.  Its  specific  gravity  is  4.95,  and  its  atomic 
weight  is  127.  It  is  slightly  volatile  at  ordinary 
temperatures,  it  melts  at  115°  C.,  and  boils  at  200°. 
Its  vapor  has  a  magnificent  violet  color ;  to  which, 
from  the  Greek  word  meaning  violet,  it  owes  its 
name. 

EXPERIMENT  59. — Put  a  fragment  of  iodine  in 
the  bottom  of  a  dry  test-tube,  and  heat  gently  over 
a  flame.  The  violet  vapors  will  recondense  in  the 
upper  and  cooler  part  of  the  tube.  This  process, 
by  which  a  solid  is  vaporized  and  again  condensed 
without  passing  through  the  intermediate  liquid 
state,  is  called  sublimation.  The  best  commercial 
iodine  is  commonly  labeled  "  resublimed." 

EXPERIMENT  60. — Into  the  test-tube  used  for 
the  last  experiment,  pour  a  little  alcohol.  The  io- 
dine will  presently  dissolve.  The  solution  thus  ob- 
tained is  much  used  in  medicine  under  the  name  of 
"  tincture  of  iodine."  Water  will  dissolve  only  a 
mere  trace  of  the  element. 

EXPERIMENT  61. — Make  a  little  starch-paste  by 
warming  common  starch  with  water.  A  drop  of 
tincture  of  iodine  added  to  this  will  strike  a  deep- 
blue  color.  This  is  the  ordinary  test  for  free  io- 
dine.* Conversely,  iodine  is  a  test  for  starch. 

*  Refer  back  to  the  test  for  ozone  in  the  chapter  on  oxygen. 


130  INORGANIC  CHEMISTRY. 

EXPERIMENT  62. — Mix  a  solution  of  potassium 
iodide  with  some  of  the  starch-paste.  Now  add 
a  few  drops  of  chlorine-water.  Iodine  will  be 
set  free,  and  the  mixture  will  become  blue.  Chlo- 
rine and  bromine  both  liberate  iodine  from  io- 
dides. 

Iodine  and  its  compounds  are  much  used  in 
medicine,  in  photography,  and  in  the  preparation 
of  certain  aniline  dyes.  In  general,  the  com- 
pounds resemble  those  of  chlorine  and  bromine. 
Hydriodic  acid,  HI,  is  a  colorless  gas  soluble  in 
water.  But  one  oxide  is  known — the  pentoxide, 
I2O5,  which  is  produced  easily  by  the  direct  oxi- 
dation of  iodine.  There  are  also  two  acids,  iodic 
and  periodic,  HIO3  and  HIO4,  which  are  much 
more  stable  than  the  corresponding  compounds  of 
chlorine. 

With  nitrogen  iodine  forms  a  compound  which 
is  curiously  explosive.  Its  formula  is  probably  NI3, 
although  it  is  rarely  obtained  perfectly  pure. 

EXPERIMENT  63. — Pour  a  little  strong  ammonia- 
water  over  some  powdered  iodine,  and  let  it  stand 
for  half  an  hour.  Filter  the  black  sediment  off 
upon  several  small  niters,  and  spread  these,  while 
still  wet,  at  a  distance  from  each  other  to  dry. 
When  the  powder,  which  is  impure  nitrogen  io- 
dide, is  thoroughly  dry,  it  will  explode  even  at 
the  touch  of  a  feather.  It  is  by  far  the  most  sen- 
sitive detonating  substance  known  ;  and  never  more 
than  a  few  grains  of  it  should  be  prepared  at  a 
time. 

The  following  table  of  formulae  may  serve  to  as- 
sist the  memory  concerning  the  chief  compounds  of 
F,  Cl,  Br,  and  I : 


THE  CHLORINE  GROUP. 


HF 

HC1 

"HPIO 

HBr 

HRrO 

HI 

HriOo 

HClOo 

HRrO<, 

HTO, 

Hrio, 

HRrfh 

HTfX, 

Q  of) 

Q  Do 

Qr\ 

3v_/4 

T»OK 



NC13 

ecu 

NBrs 
CBr4 

NI8 
CI4 

As  we  go  on,  we  shall  find  that  these  elements 
always  form  closely  similar  compounds. 


CHAPTER  XV. 

SULPHUR. 

SULPHUR,  selenium,  and  tellurium  are  three  biv- 
alent elements  which,  together  with  oxygen,  form 
a  second  well-marked  natural  group.  A  few  formu- 
las will  show  their  chemical  similarity  : 


H20 
HoOo 

H2S 

He 

H2Se 

H2Te 

COa 

CSo 

OOa  (ozone) 

S02 

cr) 

SeOa 

TeOa 

Tp>O 

H  <^O 

•LJ  cpr» 

HTp«n 

H^O 

HQpO 

HT>n 

SULPHUR  occurs  abundantly  in  nature,  both  free 
and  combined.  Among  the  sulphides*  we  find  the 
chief  ores  of  lead,  mercury,  silver,  copper,  and  anti- 
mony, and  some  of  the  commonest  minerals  con- 
taining iron  and  zinc.  Calcium  sulphate,  or  gyp- 
sum, exists  in  vast  quantities,  and  other  sulphates  are 
frequently  met  with.  Sulphur  is  also  found  in  such 
animal  substances  as  hair,  albumen,  etc.,  and  in  the 
pungent  oils  to  which  garlic,  mustard,  and  horse- 
radish owe  their  biting  flavors.  The  blackening  of 


*  Formerly  called  sulphurets. 


SULPHUR. 


133 


silver  spoons  by  eggs  is  due  to  the  formation  of  sil- 
ver sulphide  by  the  sulphur  which  the  eggs  contain. 
Nearly  all  the  sulphur  of  commerce  is  native 
sulphur  from  Southern  Italy  and  Sicily.  It  is  of 
volcanic  origin,  and  occurs  sometimes  in  brilliant 
crystals,  but  more  commonly  in  opaque  masses 
mixed  with  dirt.  By  a  simple  process  it  is  melted 
out  from  its  earthy  impurities,  after  which  it  is  re- 
fined by  distillation,  as  shown  in  Fig.  32.  The  vapor 


FIG.  32. — Distillation  of  Sulphur. 

passes  from  the  retort  into  a  large  brick  chamber, 
in  which  it  condenses  at  once  to  the  fine  powder 
known  as  "  flowers  of  sulphur."  By  degrees  the 
walls  of  the  chamber  become  heated,  and  then  a 


134  INORGANIC  CHEMISTRY. 

part,  or  even  all,  of  the  sulphur  assumes  the  liquid 
state  and  is  drawn  off  into  molds.  This  gives  the 
round  sticks  called  "  roll-brimstone."  Still  another 
variety  of  sulphur,  "  lac  sulphur,"  is  prepared  by 
adding  hydrochloric  acid  to  a  solution  of  calcium 
sulphide.  It  is  precipitated  as  a  fine  white  powder 
which  is  used  in  medicine. 

Sulphur  is  ordinarily  a  yellow,  brittle  solid,  with- 
out taste  or  odor.  It  dissolves  in  carbon  disulphide, 
but  not  in  water;  it  melts  at  114.5°  C.,  and  boils  at 
448°.  Its  atomic  weight  is  32 ;  but  below  500°  the 
density  of  its  vapor  is  three  times  this,  or  96.  Be- 
tween 800°  and  1,000°  the  vapor  density  becomes 
normal,  and  agrees  with  the  atomic  weight.  Hence, 
applying  Avogadro's  law,  and  remembering  that  the 
vapor  density  is  always  half  the  molecular  weight, 
we  find  that  at  ordinary  temperatures  the  sulphur- 
molecule  is  S6,  but  at  very  high  temperatures  it  be- 
comes S2. 

Sulphur  is  a  remarkable  example  of  allotropy. 
The  natural  crystals  are  rhombic  octahedra,  and 
similar  crystals  are  deposited  from  a  solution  of  the 
element  in  carbon  disulphide.  Their  specific  grav- 
ity is  2.07.  From  fusion,  however,  sulphur  solidi- 
fies in  slender  prisms  of  sp.  gr.  1.98.  Accordingly, 
sulphur  is  said  to  be  dimorphous.  A  body  capable 
of  crystallizing  in  three  distinct  forms  would  be  tri- 
morphous. 

EXPERIMENT  64.— Carefully  melt  a  little  sulphur 
in  a  test-tube,  and  let  it  stand  quietly  to  cool,  Crys- 
tals, like  slender  needles,  will  shoot  out  from  the 
sides  of  the  tube  toward  the  center,  and  form  a 
solid  interlacing  mass.  A  better  plan,  perhaps,  is 
to  melt  a  considerable  quantity  of  sulphur  in  an 


SULPHUR.  135 

earthen  crucible,  and  let  it  cool  until  a  crust  forms 
over  the  top.  Upon  breaking  this  crust  and  pour- 
ing out  the  still  fluid  material  beneath  it,  the  cruci- 


FIG.  33. — Crystals  of  Sulphur,  both  forms. 

ble  will  be  found  to  be  lined  with  slender  prismatic 
crystals.  This  is  a  general  method  for  crystalliz- 
ing substances  from  fusion.  Bismuth,  thus  treated, 
yields  superb  crystals. 

A  third  variety  of  sulphur,  plastic  sulphur,  may 
be  obtained  by  pouring  melted  sulphur  into  cold 
water. 

EXPERIMENT  65. — Fill  a  test-tube  half  full  of  sul- 
phur, and  heat  gradually  over  a  flame.  At  114.5° 
it  will  melt  to  a  clear,  amber-colored  fluid,  which, 
as  the  temperature  rises,  will  become  darker  in  tint 
and  quite  viscid.  At  230°  it  will  be  almost  black, 
and  so  thick  that  the  test-tube  may  be  inverted 
without  a  drop  running  out.  Above  250°  it  again 
will  become  fluid,  and  if  it  be  poured  into  cold 
water  it  will  assume  the  form  of  a  brownish  mass 
which  may  be  worked  between  the  fingers  like  put- 
ty, or  even  drawn  out  into  slightly  elastic  threads. 
By  much  kneading,  or  even  by  standing  for  a  few 
days,  the  plastic  mass  will  crumble  and  pass  back 
into  ordinary  sulphur. 

Sulphur  combines  easily  with  most  of  the  other 
elements.  In  Experiment  i  its  union  with  a  metal 

7 


136  INORGANIC  CHEMISTRY. 

was  shown ;  and  at  this  point  the  pupil  may  advan- 
tageously repeat  the  experiment  with  the  three  met- 
als copper,  iron,  and  zinc.*  The  element  has  many 
uses.  It  is  an  ingredient  of  gunpowder,  of  matches, 
and  of  vulcanized  rubber ;  and  immense  quantities 
of  it  are  consumed  in  the  manufacture  of  sulphuric 
acid,  and  in  the  bleaching  of  silks  and  woolens. 

With  hydrogen,  sulphur  combines  like  oxygen 
in  two  proportions,  forming  H2S  and  H2S2.  The 
latter  is  an  oily  liquid,  of  nauseous  odor  and  power- 
ful bleaching  properties,  but  having  only  theoreti- 
cal importance. 

Hydrosulphuric  acid,  also  known  as  sulphhy- 
dric  acid,  or  sulphuretted  hydrogen,  is  a  colorless 
gas  having  the  peculiar  odor  of  rotten  eggs.  Its 
density,  as  shown  by  the  formula  H2S,  is  17;  and 
it  burns  with  a  blue  flame  to  form  sulphur  dioxide 
and  water :  H2S  +  $O  =  H2O  +  SO2.  In  the  con- 
centrated state  it  is  poisonous  to  inhale  ;  and  it  may 
be  reckoned  as  one  of  the  more  objectionable  prod- 
ucts of  animal  putrefaction.  For  laboratory  pur- 
poses it  is  usually  prepared  by  the  action  of  dilute 
sulphuric  acid  upon  iron  sulphide,  which  latter  sub- 
stance is  made  by  heating  together  iron-filings  and 
sulphur. 

EXPERIMENT  66.  —  Place  some  iron  sulphide, 
broken  into  small  fragments,  in  the  flask  previously 
used  for  the  preparation  of  hydrogen,  and  pour 
over  it  some  dilute  sulphuric  acid.  The  hydrosul- 

*  A  mixture  of  32  parts  of  flowers  of  sulphur  with  65  parts  of  zinc 
in  the  form  known  as  "  zinc-dust,"  may  be  ignited  by  a  match.  It 
burns  with  a  beautiful  greenish  flame,  leaving  a  bulky  residue  of  yel- 
lowish-white zinc  sulphide.  In  a  confined  space  the  combustion  is  ex- 
plosive. 


SULPHUR. 


137 


phuric  acid  will  be  given  off  with  effervescence,  and 
may  be  collected  by  displacement.  Verify  its  com- 
bustibility as  in  the  case  of  hydrogen,  bearing  in 
mind  that  it  also  makes  an  explosive  mixture  with 
air.  By  passing  a  stream  of  the  gas  through  water 
a  solution  of  it  may  be  obtained,  which  will  be  of 
use  in  subsequent  experiments.  The  present  experi- 
ment may  be  represented  by  the  subjoined  equation  : 

FeS  +  H3S04  =  FeS04  +  HaS. 

Hydrosulphuric  acid  is  largely  used  as  a  test  re- 
agent in  qualitative  analysis,  for  the  precipitation, 
as  sulphides,  of  lead,  copper,  tin,  antimony,  bismuth, 
cadmium,  etc. 

EXPERIMENT  67. — Dissolve  in  water,  in  separate 
test-tubes  or  beaker-glasses,  fragments  of  lead  ni- 
trate, copper  sulphate,  cadmium  sulphate,  and  tar- 
tar emetic,  and  acidulate  each  solution  with  a  few 
drops  of  hydrochloric  acid.  Now  pass  into  each  a 
few  bubbles  of  H2S,  or  add 
a  little  of  the  solution  of 
the  gas  previously  prepared, 
and  note  the  character  of 
the  precipitates  which  form 
(Fig.  34).  Solutions  con- 
taining salts  of  other  metals 
may  also  be  tested.  Some 
will  yield  precipitates  and 
some  will  not ;  for  example, 

if   we    have    compounds   of    FIG.  34.— Precipitation  by  HaS. 

lead  and  iron  dissolved  to- 
gether, we  may  throw  down  all  the  lead  as  solid 
lead  sulphide,  and  filter  it  off,  leaving  the  iron  in 
solution.      Thus  the  two  metals  can  be  easily  and 


138 


INORGANIC  CHEMISTRY. 


completely  separated  from  each  other.  Two  equa- 
tions will  illustrate  the  nature  of  these  precipita- 
tions : 

CuSO4  +  H2S  =  CuS  +  H2S04. 

Pb(NO3)2  +  H2S  =  PbS  +  2HNO3. 

EXPERIMENT  68. — Drop  a  solution  of  H2S  upon 
a  bright  silver  coin  or  a  bit  of  bright  copper.  A 
sulphide  will  be  formed,  the  metal  will  be  black- 
ened, and  hydrogen  will  be  set  free : 

Cu  +  H2S  =  CuS  +  H2. 

Ag2  +  H2S  =  AgaS  +  H2. 

Sulphuretted  hydrogen  occurs  in  many  mineral 
springs.  The  Blue  Lick,  White  Sulphur,  and  Sha- 
ron waters  all  emit  the  gas  copiously ;  and  to  it  some 
of  their  medicinal  value  is  ascribed. 

Four  oxides  of  sulphur  are  known — namely,  SO2, 
SO3,  S2O3,  and  S2O7.  Only  the  first  two  are  impor- 
tant. Sulphur  dioxide,  SO2,  is  formed  whenever 
sulphur  burns,  and  to  it  the  familiar  "  brimstone 
odor  "  is  due.  It  is  a  colorless  gas,  of  density  32, 
and  is  prepared  either  by  the  direct  combustion 
of  sulphur,  or  by  roasting  iron  pyrites,  FeS2,  in  a 
stream  of  air.  It  is  used  in  the  manufacture  of  sul- 
phuric acid,  as  a  disinfectant,  and  for  bleaching 
silk,  wool,  feathers,  and  straw,  which  would  be  in- 
jured by  chlorine.  It  also  serves  to  check  the  fer- 
mentation of  wine  or  cider.  As  a  disinfectant  its 
mode  of  action  is  exactly  opposite  to  that  of  chlo- 
rine. The  latter  in  most  cases  oxidizes  the  bodies 
which  are  to  be  destroyed,  while  sulphur^  dioxide 
withdraws  oxygen  from  them.  As  a  bleaching 
agent,  however,  it  seems  to  combine  with  the  color- 
ing-matter to  form  an  unstable  compound  ;  and  any 


SULPHUR. 

substance  which  destroys  the  latter  will  bring  the 
color  back  again.  For  laboratory  purposes  sulphur 
dioxide  may  be  conveniently  prepared  as  follows : 

EXPERIMENT  69. — Heat  some  scraps  of  copper 
with  strong  sulphuric  acid  in  the  flask  which  was 
previously  used  for  making  chlorine.  When  a  tol- 
erably high  temperature  has  been  reached,  sulphur 
dioxide  will  be  freely  evolved,  according  to  the  sub- 
joined reaction : 

Cu  +  2H2SO4  =  CuSO4  4-  SOa  +  2HaO. 

The  gas  may  be  collected  over  mercury,  or  by  dis- 
placement. Instead  of  copper,  charcoal  may  be 
used,  but  the  sulphur  dioxide  produced  will  be  im- 
pure. 

EXPERIMENT  70. — Pass  a  stream  of  the  gas  from 
Experiment  69  into  cold  water.  It  will  be  absorbed, 
and  with  the  solution,  which  will  have  the  charac- 
teristic odor  of  SO2,  some  bleaching  experiments, 
like  Experiments  50  and  54,  may  be  tried.  Sulphur 
dioxide  bleaches  only  in  presence  of  moisture. 

The  aqueous  solution  of  sulphur  dioxide  may  be 
formulated  thus :  H2O  +  SO2  =  H2SO3.  The  latter 
symbol  is  that  of  sulphurous  acid,  which,  like  car- 
bonic acid,  unites  with  bases  to  form  two  sets  of 
salts.  For  example,  we  have — 

NaHSO3  KHSO3 

Na2S03  K2SO3 

CaSO3,  etc. 

The  salts  which  retain  half  of  their  hydrogen  are 
known  as  acid  sulphites,  or  sometimes  as  ^sulphites. 
Those  in  which  the  replacement  of  hydrogen  is  com- 
plete are  called  normal or  neutral  salts.  The  sodium 


I4o  INORGANIC  CHEMISTRY. 

hydrogen  sulphite,  NaHSO3,  is  sometimes  used  in 
paper-mills  and  chlorine  bleacheries,  to  neutralize 
any  excess  of  chlorine  which  might,  if  retained  in 
the  fabric,  tend  to  weaken  its  fibers.  Substances 
used  for  this  purpose  are  termed  "  antichlors." 

Sulphur  trioxide,  SO3,  may  be  prepared  by  the 
oxidation  of  SO2  under  peculiar  circumstances,  or 
by  heating  a  compound  known  as  pyrosulphuric  acid, 
H2S2O7.  It  usually  forms  long,  silky,  white  needles, 
which  unite  with  water,  developing  great  heat,  to 
generate  sulphuric  acid  : 

HaO  +  SO3  =  HaSO4. 

The  similarity  between  this  reaction  and  the  one 
which  yields  sulphurous  acid  should  be  carefully 
noted.  Although  H2SO4  is  one  of  the  strongest 
acids  known,  SO3  does  not  even  redden  litmus- 
paper.  By  some  chemists  these  acid-forming  oxides 
are  termed  anhydrides.  Thus  we  have — 

NaO6,  nitric     anhydride,  which  with  water  yields  HNO3. 
IaO6,    iodic  "  "         "         "          "       HIO3. 

COa,    carbonic       "  "        "        "         "      H2CO3. 

SOa,     sulphurous  "  "         "         "          "       H2SO3. 

SO3,     sulphuric      "  "        "        "          " 


cid.  ) 

i 


CHAPTER  XVI. 

SULPHUR — (continued'). 

SULPHUR  is  remarkable  for  the  number  of  acids 
which  it  forms  by  combination  with  hydrogen  and 
oxygen.  They  are  as  follow  : 

1.  HaSOa,   Hyposulphurous  acid. 

2.  HaSO3,   Sulphurous 

3.  HaSO4,   Sulphuric 

4.  HaSaOT,  Pyrosulphuric 

5.  HaSaOs,  Thiosulphuric 

6.  HaSaOe,  Dithionic 

7.  HaSaOe,  Trithionic 

8.  HaS4O6,  Tetrathionic 

9.  HaSsOe,  Pentathionic  * 

Most  of  these  are  unimportant,  and  need  no  fur- 
ther mention.  Sulphurous  acid  has  already  been 
described ;  and  thiosulphuric  acid,  which  does  not 
exist  by  itself,  is  of  consequence  only  in  one  or 
two  of  its  salts.  Sodium  thiosulphate,  commercial- 
ly known  as  "  hyposulphite  of  soda,"  is  very  largely 
used  in  the  art  of  photography.  It  serves  to  dis- 
solve out  from  the  photographic  plate  those  com- 
pounds which  have  escaped  the  action  of  light,  and 
which,  if  they  were  allowed  to  remain,  would  cause 
the  photograph  to  fade. 

*  The  existence  of  this  acid  has  lately  been  called  in  question. 


142  INORGANIC  CHEMISTRY. 

In  sulphuric  acid,  however,  we  find  a  compound 
which  is  undoubtedly  the  most  important  yet  dis- 
covered by  chemistry.  It  has  so  many  and  such 
varied  uses  that,  as  has  been  well  said,  the  advance- 
ment of  any  nation  in  civilized  arts  may  be  meas- 
ured by  the  amount  of  sulphuric  acid  which  it 
consumes.  Its  annual  production  must  be  over  a 
million  tons ;  *  and  it  is  used  in  the  manufacture  of 
all  the  other  strong  acids,  of  chlorine,  of  soda,  of 
alum,  of  phosphorus,  of  quinine,  and  of  the  more 
important  fertilizers.  It  is  also  employed  in  refin- 
ing fats  and  oils,  in  dyeing  and  bleaching,  and  as 
an  exciting  liquid  in  several  forms  of  the  galvanic 
battery.  There  is  probably  no  great  manufactur- 
ing industry  which  does  not,  directly  or  indirectly, 
make  use  of  this  acid.  In  nature  it  sometimes, 
though  rarely,  occurs  uncombined.  The  waters  of 
the  Rio  Vinagre,  in  South  America,  are  rendered 
appreciably  sour  by  its  presence ;  and  the  Oak  Or- 
chard mineral  spring  at  Medina,  New  York,  con- 
tains nearly  a  gramme  and  a  half  to  the  litre.  It  is 
also  found  to  a  quite  perceptible  extent  in  the  saliva 
of  certain  mollusks. 

Commercially,  sulphuric  acid  is  prepared  by 
oxidizing  sulphurous  acid  with  nitrous  fumes.  The 
process  is  essentially  as  follows : 

Sulphur  dioxide,  generated  by  the  combustion 
of  sulphur,  or  by  roasting  iron  pyrites  in  a  suitable 
furnace,  is  passed  into  a  large  chamber,  or  series 
of  chambers,  lined  with  sheet-lead  f  (Fig.  35).  Ni- 

*  In  Great  Britain  alone  more  than  850,000  tons  are  annually  made. 

f  Such  a  chamber  may  be  thirty  metres  long,  six  or  seven  wide,  and 
five  high ;  but  the  dimensions  and  arrangement  are  different  in  differ- 
ent places.  An  excellent  account  of  the  manufacture  is  given  in  Roscoe 
and  Schorlemmer's  "  Treatise  on  Chemistry,"  vol.  i,  pp.  319-338. 


SULPHUR. 


143 


trous  fumes,  produced  by  heating  sodium   nitrate 

with  a  little  sulphu- 

ric  acid,  enter   the 

chamber  at  the  same 

time  ;  jets  of  steam 

are  blown  in  at  sev- 

eral   points,   and    a 

thorough      draught 

of    air   is    kept    up 

throughout.        The 

sulphur         dioxide, 

meeting    the    nitric 

acid    which    enters 

the  chamber  with  it, 

becomes  oxidized  in- 

to sulphuric  acid,  in 

accordance  with  the 

following  reaction  : 


SO2 


2HNO3  =  H2SO4 
+  2NOa. 


The  NO2,  in  pres- 
ence of  steam,  oxi- 
dizes a  fresh  portion 
of  sulphur  dioxide, 
becoming  itself  re- 
duced to  NO;  thus: 

SO2  +  H2O  +  NO2  = 
H2SO4  +  NO. 

The  last  substance 
now  takes  up  an 
atom  of  oxygen  from 
the  air,  regenerating 
NO2,  but  surrenders  it  at  once  to  another  portion  of 


144 


INORGANIC  CHEMISTRY. 


the  sulphurous  acid ;  it  is  then  reoxidized  by  more 
air,  again  reduced,  again  oxidized,  and  so  on  indefi- 
nitely. Theoretically  a  very  small  amount  of  NO2 
would  serve  to  oxidize  an  infinite  quantity  of  sul- 
phurous acid  ;  but  practically  there  is  always  some 
loss,  and  fresh  fumes  are  therefore  constantly  sup- 
plied. It  will  be  seen  that  the  fumes  act  simply  as 
carriers  of  oxygen  from  the  air  to  the  mixture  of 
steam  and  SO2,  which  latter  is  being  continually 
transformed  into  sulphuric  acid  by  the  process. 
The  acid  thus  formed  condenses  on  the  floor  of  the 
chamber,  whence  it  is  drawn  off. 

This  "  chamber  acid,"  as  it  is  called,  is  a  brown- 
ish, oily  liquid  of  specific  gravity  1.55.  It  still  con- 
tains much  water,  from  which  it  is  partly  freed  by 
evaporation  in  leaden  pans  until  its  sp.  gr.  reaches 
1.71.  At  this  point  it  begins  to  attack  the  lead  ;  so 
that  further  concentration  is  effected  by  heating  in 
retorts  of  glass  or  platinum,  until  it  attains  a  sp.  gr. 
of  1.842.  It  is  now  pure  enough  for  all  commer- 
cial purposes  ;  but,  in  order  to  render  it  chemically 
pure,  it  has  to  be  distilled. 

In  its  purest  state  sulphuric  acid  is  a  colorless, 
limpid,  oily  liquid,  of  specific  gravity  1.854,  which 
boils  at  338°  centigrade,  and  freezes  at  10.5°.  The 
brown  color  of  the  commercial  acid  is  due  to  or- 
ganic matter  derived  from  the  dust  of  the  air.  It 
is  a  powerful  solvent,  attacking  many  of  the  metals 
and  converting  them  into  sulphates,  and  charring 
such  organic  substances  as  wood,  sugar,  animal 
matter,  etc.  There  is  an  easy  experiment  to  illus- 
trate this  point. 

EXPERIMENT  71. — Add  to  a  very  strong  solution 
of  white  sugar  in  water,  its  own  bulk  of  sulphuric 


SULPHUR.  145 

acid.  In  a  few  moments  it  will  blacken,  swell  up, 
and  become  a  porous  mass  of  charcoal.  The  ex- 
planation of  this  phenomenon  is  simple.  Sugar  con- 
tains carbon,  hydrogen,  and  oxygen ;  the  last  two 
being  present  in  just  the  proportions  needful  to 
form  water.  Sulphuric  acid  unites  with  water  with 
intense  avidity ;  accordingly,  it  withdraws  the  hy- 
drogen and  oxygen  from  the  sugar,  leaving  the  car- 
bon behind.  The  corrosive  action  of  sulphuric  acid 
upon  the  skin  and  upon  clothing  is  of  the  same  gen- 
eral character  as  the  foregoing. 

The  strong  affinity  of  sulphuric  acid  for  water  is 
also  indicated  by  the  fact  that  when  the  two  sub- 
stances are  mixed  great  heat  is  evolved.  This  may 
be  verified  by  experiment  in  a  test-tube  or  small 
beaker.  The  mixture,  which  often  has  to  be  made 
in  the  laboratory,  should  always  be  effected  care- 
fully;  best  by  pouring  the  acid  slowly  into  the 
water,  and  stirring  the  latter  with  a  glass  rod  at 
the  same  time.  By  allowing  gases  to  bubble 
through  strong  sulphuric  acid,  they  may  be  thor- 
oughly dried.  For  this  purpose  the  arrangement 
shown  in  Fig.  36  is  commonly  employed.  The  gas- 
stream  enters  through  the  longer  tube,  which  ex- 
tends to  the  bottom  of  the  flask,  rises  through  the 
acid,  and  issues  from  the  shorter  tube.  The  ease 
with  which  sulphuric  acid  absorbs  moisture  from 
the  air  may  be  simply  illustrated  as  follows : 

EXPERIMENT  72.— Fill  a  test-tube  one  third  full 
of  strong  sulphuric  acid,  and  carefully  mark  its  level 
on  the  side.  Let  it  stand  exposed  to  the  air  for  a 
day  or  two,  and  again  note  the  level  of  the  liquid. 
The  latter,  by  virtue  of  the  absorbed  water,  will  be 
found  to  have  increased  in  bulk  very  perceptibly. 


146 


INORGANIC  CHEMISTRY. 


The  affinity  between  sulphuric  acid  and  water  is 
really  due  to  a  distinct  chemical  action ;   for  two 


FIG.  36.— Washing-Flask  for  Gases. 

definite  compounds,  called   hydrates,  are  formed. 
Their  formulae  are  written  thus : 

H2S04,  H20, 
HaS04,  2HaO. 

At  low  temperatures  these  hydrates  crystallize  in 
characteristic  forms. 

Sulphuric  acid  was  originally  produced  by  a 
process  quite  distinct  from  that  which  is  carried  on 
in  the  leaden  chambers.  Sulphate  of  iron,  or  "  vit- 
riol," was  distilled  in  earthen  retorts,  and  an  acid 
having  the  formula  H2SO4+SO8,  or  H2S2O7,  col- 
lected in  the  receivers.  This  was  the  "oil  of  vit- 
riol "  of  the  early  chemists.  It  is  now  commonly 
known  as  "  Nordhausen  sulphuric  acid,"  from  the 


SULPHUR.  147 

town  in  Saxony  at  which  it  is  still  made.  It  is  also 
called  "  fuming  sulphuric  acid,"  from  the  fact  that 
it  emits  white  fumes  of  sulphur  trioxide.  The  latter 
substance  may  be  expelled  by  heating,  when  H2SO4 
remains  behind.  By  many  chemists  the  compound 
H2S2O7  is  regarded  as  a  distinct  acid  of  sulphur,  and 
to  it  the  name  of  pyrosulphuric  acid  is  applied. 

Like  sulphurous  and  carbonic  acids,  sulphuric 
acid  is  dibasic — that  is,  it  contains  two  hydrogen- 
atoms  which  are  replaceable  by  bases.  Thus  we 

have — 

KHSO4  NaHSO4 

K3SO4  NaaSO4 

CaSO4,  etc. 

The  sulphates  of  sodium,  calcium,  magnesium,  ba- 
rium, iron,  zinc,  copper,  etc.,  are  all  important  com- 
pounds, which  will  be  described  in  their  proper 
connection  further  on. 

In  the  ordinary  process  for  making  sulphuric 
acid,  white  crystals,  called  "  lead-chamber  crystals," 
are  sometimes  formed.  Their  formation,  which  oc- 
curs only  when  there  is  a  deficiency  of  steam,  may 
be  illustrated  on  a  small  scale  as  follows : 

EXPERIMENT  73.— Into  a  stoppered  bottle,  con- 
taining dry  sulphur  dioxide,  introduce  a  glass  rod 
moistened  with  nitric  acid.  Red  fumes  will  appear, 
and  after  a  short  time  white  crystals  will  be  de- 
posited on  the  sides  of  the  glass.  Upon  the  addi- 
tion of  water  they  will  dissolve  with  effervescence, 
giving  off  red  fumes,  and  yielding  sulphuric  acid. 
Their  formula  is  HSO3NO2,  and  they  give  us  an 
important  clew  to  the  constitution  or  structure  of 
the  sulphuric-acid  molecule. 

In  SO2  we  have  a  compound  which  may  be  re- 


148  INORGANIC  CHEMISTRY. 

garded  as  a  bivalent  radicle.  It  unites  with  one 
atom  of  bivalent  oxygen  to  form  SO3,  and  also  with 
two  atoms  of  univalent  chlorine  to  produce  sul- 
phuryl  chloride,  SO2C12.  With  O  and  H^O  it  yields 
sulphuric  acid,  which  may  be  written  structurally  : 


In  this  formula  we  meet  with  a  peculiar  group  of 
atoms,  which  is  essentially  water  minus  half  its  hy- 
drogen, and  in  all  acid  molecules  this  group  occurs. 
It  is  called  hydroxyl,  and  is  necessarily  univalent, 
since  the  oxygen  in  it  is  only  half  satisfied.  Hydro- 
gen dioxide,  H2O2,  is  probably  hydroxyl  in  the  un- 
combined  state  ;  (OH)2  being  a  molecule  similar  to 
H2,  C12,  and  (CN)2.  Nitric  acid,  HNO3,  is  struct- 
urally OH-NO2,  the  NO2  being  another  univalent 
radicle  of  great  importance.  Using  these  radicles, 
SO2U,  NO2,  and  OH1,  we  may  now  write  the  follow- 
ing structural  formulae  : 

S03=0  S°2<OH  SO<SH 

Sulphur  trioxide.  Sulphuric  acid.  Thiosulphuric  acid. 

/Cl  /OH  /NO, 

soJxci  so^q  so,XQH 

Sulphuryl  chloride.  Chlorosulphonic  acid.          Lead-chamber  crystals. 

SO<OH 
)0 

SOa\OH 

Pyrosulphuric  acid. 

Some  of  these  compounds  have  only  theoretical 
importance,  and  need  not  be  specially  described. 

With  nitrogen,  chlorine,  bromine,  and  iodine, 
sulphur  forms  various  compounds  ;  but  only  one  of 
them,  the  chloride,  S2C12,  needs  further  mention  here. 


SULPHUR.  I49 

This  substance  is  a  volatile  yellow  liquid,  produced 
by  the  direct  union  of  its  elements.  It  is  somewhat 
used  in  a  process  for  vulcanizing  rubber. 

With  carbon,  sulphur  yields  two  compounds, 
CS  and  CS2,  analogous  to  CO  and  CO2.  The  disul- 
phide,  CS2,  is  produced  by  heating  charcoal  to  red- 
ness in  a  stream  of  sulphur- vapor.  It  is  a  colorless, 
brilliant  liquid  of  sp.  gr.  1.29,  which  boils  at  46°. 
Its  odor  suggests  that  of  ether,*  and  its  vapor  forms 
an  explosive  mixture  with  air.  It  is  very  combus- 
tible, and  burns  according  to  the  equation — 

CS2  +  6O  =  CO2  +  2SO2. 

Its  practical  importance  depends  upon  its  solvent 
properties,  it  having  the  power  of  dissolving  easily 
such  substances  as  sulphur,  phosphorus,  rubber,  fats, 
and  oils.  A  solution  of  rubber  in  it  gives  a  conven- 
ient water-proof  varnish  ;  and  it  is  also  used  on  the 
large  scale  for  the  extraction  of  fats  from  animal 
refuse.  The  number  of  its  useful  applications  seems 
to  be  constantly  increasing. 

SELENIUM,  atomic  weight  79,  is  an  element  which 
is  found  as  an  occasional  impurity  of  sulphur,  and  as 
a  constituent  of  certain  rare  minerals.  Its  specific 
gravity  varies  from  4.25  to  4.80,  and  like  sulphur  it 
is  allotropic.  It  has  few  uses,  and  these  depend  upon 
its  remarkable  electrical  properties. 

Seleniuretted  hydrogen,  H2Se,  is,  like  H2S,  a  gas 
of  intolerably  nauseous  odor.  The  dioxide,  SeO2,  is 
a  white  solid  which  unites  with  water  to  form  sele- 
nious  acid,  H2SeO3.  Selenic  acid,  H2SeO4,  is  very 
similar  to  sulphuric  acid,  only  not  so  strong.  The 

*  Commercial  carbon  disulphide  has  a  nauseous  odor,  which  is  due 
to  impurities. 


150  INORGANIC  CHEMISTRY. 

selenates  are  isomorphous  with  the  sulphates — that  is, 
they  crystallize  in  precisely  the  same  forms. 

TELLURIUM  is  another  rare  element  having  semi- 
metallic  properties.  It  is  tin-white,  brittle,  and  has 
a  sp.  gr.  of  6.25.  It  occurs  in  nature  free,  and  also 
combined  as  tellurides  with  lead,  bismuth,  gold, 
silver,  and  mercury.  The  tellurides  of  gold  and 
silver  are  important  ores,  especially  in  Colorado. 
The  compounds  of  tellurium  in  general  resemble 
those  of  selenium  and  sulphur.  For  example,  H2Te 
is  a  gas,  and  H2TeO3  and  H2TeO4  are  characteristic 
acids.  No  uses  have  yet  been  found  for  either  the 
element  or  its  compounds. 


CHAPTER  XVII. 

PHOSPHORUS. 

JUST  as  sulphur,  selenium,  and  tellurium  belong 
to  the  oxygen  group  of  elements,  so  also  phospho- 
rus, arsenic,  antimony,  bismuth,  and  vanadium  may 
be  classed  with  nitrogen.  Only  two  of  these  sub- 
stances, however,  phosphorus  and  arsenic,  will  be 
considered  among  the  non-metallic  elements. 

Phosphorus  exists  in  nature  only  in  the  com- 
bined state.  It  is  found  in  many  rocks,  in  all  fertile 
soils,  in  plants,  and  in  animals.  Human  bones  con- 
tain more  than  half  their  weight  of  calcium  phos- 
phate, Ca3P2O8 ;  and  in  other  combinations  phospho- 
rus is  an  important  constituent  of  nervous  matter 
and  of  the  brain.  Calcium  phosphate  is  one  of  the 
commoner  minerals,  apatite,  and  is  often  found  in 
large  beds ;  and  the  phosphates  of  lead,  iron,  alumi- 
num, manganese,  copper,  uranium,  and  magnesium 
form  well-known  mineral  species. 

The  element  itself  was  discovered  by  Brand  of 
Hamburg,  in  1669.  It  is  now  prepared  on  a  large 
scale  from  bone-ash ;  or  from  sombrerite,  an  im- 
pure calcium  phosphate  found  in  West  Indian  gua- 
no. The  powdered  material,  which  is  essentially 
Ca3P2O8,  is  mixed  with  sulphuric  acid  and  water, 
when  calcium  sulphate  is  formed  and  deposited  as 


152  INORGANIC  CHEMISTRY. 

an  insoluble  white  sediment.  The  remaining-  liquid, 
which  is  drawn  off  clear  from  this  precipitate,  con- 
tains an  acid  calcium  phosphate,  CaHPO4,  and  is 
concentrated  by  evaporation  to  a  thick  sirup.  This 
is  mixed  with  powdered  charcoal,  thoroughly  dried, 
and  distilled  in  an  earthen  retort.  Phosphorus  is 
set  free,  vaporized,  and  recondensed  under  cold 
water.  It  is  finally  cast  into  sticks,  and  sent  in  this 
form  into  commerce. 

As  ordinarily  seen,  phosphorus  is  a  yellowish- 
white,  waxy  solid,  of  specific  gravity  1.837.  It  melts 
at  44.2°,  and  boils  at  290°,  giving  a  vapor  of  which 
the  density  is  62,  or  double  the  atomic  weight,  _^-Tfie 
molecule  of  phosphorus,  therefore,  is  P4.  Phosphorus^ 
is  highly  inflammable,  and  on  this  account  it  is  used 
in  enormous  quantities  for  the  manufacture  of  fric- 
tion matches.  In  handling  it,  care  must  be  taken 
that  it  does  not  ignite  in  contact  with  the  skin,  for 
the  burns  which  it  produces  are  very  painful,  and 
troublesome  to  heal.  It  should  never  be  cut  except 
under  water ;  and,  indeed,  it  is  always  kept  under 
water  to  protect  it  from  oxidation.  Exposed  to 
the  air  at  low  temperatures,  it  oxidizes  slowly,  and 
the  chemical  action  which  thus  takes  place  gen- 
erates a  feeble  light.  Hence,  phosphorus  becomes 
luminous  in  the  dark  ;  whence  its  name,  which  sig- 
nifies "  light-bearer/'  Whenever  we  rub  a  match 
over  the  palm  of  the  hand  in  the  dark,  we  recognize 
its  luminous  property.  Although  it  is  insoluble  in 
water,  phosphorus  dissolves  slightly  in  olive-oil  and 
in  ether,  and  freely  in  carbon  disulphide.  From  its 
solution  in  the  last-named  liquid  it  may  be  obtained 
in  crystals. 

EXPERIMENT  74. — Dissolve  a  bit  of  phosphorus 


PHOSPHORUS.  153 

in  CS2,  and  pour  the  solution  over  a  piece  of  un- 
glazed  paper.  In  a  few  moments  the  disulphide 
will  evaporate,  leaving  the  phosphorus  spread  over 
the  paper  in  a  very  finely  divided  state.  Under 
these  circumstances  it  will  ignite  spontaneously, 
and  the  paper  will  burst  into  flame. 

EXPERIMENT  75. — Cover  a  bit  of  phosphorus,  no 
larger  than  a  pea,  with  about  a  teaspoonful  of  finely 
powdered  bone-black  or  lamp-black.  The  oxygen 
condensed  by  the  carbon  will  presently  cause  the 
phosphorus  to  ignite. 

When  ordinary  phosphorus  is  heated  to  240°  in 
an  atmosphere  free  from  oxygen,  it  becomes  convert- 
ed into  an  extraordinary  allotropic  form.  This  is  a 
dark-red  powder,  which  is  opaque,  insoluble  in  CS2, 
non-luminous,  and  uninflammable.  Its  specific  grav- 
ity is  2.1 1  ;  and  it  may  be  dissolved  in  melted  lead ; 
from  which,  upon  cooling,  it  will  separate  out  in 
black  crystals  of  metallic  luster,  and  specific  grav- 
ity 2.34.  It  is  odorless,  whereas  common  phos- 
phorus has  a  faint  odor  resembling  that  of  garlic ; 
and  it  is  not  poisonous,  although  the  other  variety 
is  a  violent  corrosive  poison.  Many  rat  and  bug 
poisons  are  merely  pastes  containing  ordinary  phos- 
phorus ;  and  children  have  died  in  consequence  of 
nibbling  the  tips  off  of  common  friction  matches. 
By  heating  to  260°,  red  phosphorus  may  be  retrans- 
formed  into  the  common  variety.  Very  recently 
another  modification  of  phosphorus  has  been  de- 
scribed by  Remsen  and  Reiser.  It  is  a  white,  flaky 
substance,  produced  by  distilling  common  phos- 
phorus in  an  atmosphere  of  hydrogen.  In  some 
respects  it  is  analogous  to  flowers  of  sulphur,  so 
that  "  flowers  of  phosphorus  "  would  be  a  fair  name 


154 


INORGANIC  CHEMISTRY. 


for  it.  A  black  phosphorus  has  also  been  obtained 
by  The"nard. 

Although  phosphorus  forms  three  compounds 
with  hydrogen,  only  one  of  them,  PH3,  has  any  par- 
ticular importance.  This  substance,  phosphine,  is  a 
colorless  gas,  having  a  very  disagreeable  odor,  and 
strongly  resembling  ammonia,  NH3,  in  its  structure 
and  chemical  relations.  Its  formation  is  beautifully 
illustrated  in  the  following  experiment: 

EXPERIMENT  76. — Arrange  a  small  flask  and  de- 
livery-tube, as  in  Fig.  37,  and  fill  it  nearly  full  of  a 
solution  of  either  caustic  soda  or  caustic  potash. 


FIG.  37. — Preparation  of  PH3. 

Milk  of  lime,  a  mixture  of  lime  and  water,  will  do 
nearly  as  well.  Add  to  the  solution  a  few  bits  of 
phosphorus,  and  pour  upon  its  surface  a  dozen 
drops  of  ether.  The  vapor  of  the  latter  merely 
serves  as  an  aid  in  expelling  from  the  flask  the  oxy- 
gen of  the  air.  Upon  boiling  the  solution,  PH3  will 
be  evolved,  and  each  bubble  of  the  gas,  on  rising 
from  the  water  of  the  water-pan,  will  ignite  with  a 
brilliant  flash,  and  form  a  beautiful  white  ring  of 
smoke.  The  absolutely  pure  gas  is  not  spontane- 


PHOSPHORUS. 


155 


ously  inflammable ;  this  property  being  really  due 
to  the  presence,  as  an  impurity,  of  traces  of  P2H4. 
Phosphine  may  also  be  formed  by  throwing  calcium 
phosphide  into  water,  when  the  same  inflammable 
gas-bubbles  will  appear. 

There  are  two  oxides  of  phosphorus,  P2O8  and 
P2O5,  analogous  to  N2O3  and  N2O5.  The  first  is 
formed  when  phosphorus  is  oxidized  slowly,  the 
latter  is  the  sole  product  of  the  combustion  of  the 
element.  The  one  unites  with  water  to  form  phos- 
phorous acid,  while  from  the  other,  under  like  cir- 
cumstances, phosphoric  acid  is  derived.  The  white 
smoke  produced  in  Experiments  21  and  76  consisted 
of  the  pentoxide,  which  substance  is  chiefly  remark- 
able for  its  intense  affinity  for  water.  It  is  by  far 
the  most  powerful  dehydrating  agent  known. 

Phosphorus  forms  three  distinct  acids,  as  fol- 
low : 

Hypophosphorous  acid,  H8POa. 

Phosphorous  "     H3PO3. 

Phosphoric  "     H3PO4. 

Salts  corresponding  to  the  first  acid,  hypophos- 
phites,  are  produced  by  the  action  of  alkalies  upon 
phosphorus.  One  was  formed  in  Experiment  76, 
and  remained  in  solution.  Several  hypophosphites 
are  used  medicinally.  Phosphorous  acid  and  the 
phosphites  are  unimportant,  except  theoretically. 

Phosphoric  acid,  the  highest  of  the  acids  of  phos- 
phorus, is  remarkable  because  of  its  existence  in 
three  distinct  varieties  having  different  formulas. 
These  may  be  represented  simply  as  being  formed 
by  the  union  of  P2O5  with  one,  two,  and  three  mole- 
cules of  water  successively,  as  shown  in  the  sub- 
joined equations : 


156  '  INORGANIC  CHEMISTRY. 

P2O6  4-  H2O  =P2H2O«  =  2HPO3,        w^taphosphoric  acid. 
P2O6  +  2H2O  =  P2H4O7,  /j/r0phosphoric     " 

P2O6  +  3H2O  =  P2H8O8  =  2H8PC>4, 


The  salts  of  these  acids  are  called 
/j/wphosphates,  and  0r/&?phosphates  respectively, 
and  they  differ  from  each  other  in  many  particulars. 
Orthophosphoric  acid  is  especially  interesting  as 
the  first  instance  we  have  met  with  of  a  tribasic 
acid.  Thus  it  forms  three  salts  with  sodium,  as 
follows  : 

NaH2PO4. 

Na2HPO4. 

Na8P04. 

All  the  more  common  phosphates,  such  as  calcium 
phosphate,  CasII(PO4)2,  are  orthophosphates.  Such 
salts  as  CauHPO4  and  KBaiiPO4  are  called  double 
salts;  and  some  triple  phosphates  also  are  known. 
For  example,  NaAmHPO4,  sodium  ammonium  hy- 
drogen phosphate,  is  a  triple  salt.  The  last  sub- 
stance is  much  used  in  blow-pipe  analysis  under  the 
name  of  microcosmic  salt,  or  salt  of  phosphorus. 

The  compounds  of  phosphorus  with  the  elements 
of  the  chlorine  group  have  very  great  theoretical 
interest.  Except  in  the  case  of  the  fluoride,  they 
are  formed  by  the  direct  union  of  the  elements,  and 
have  the  following  formulae  : 

PF6. 

PCI..  PCI.. 

PBr3.  PBr6. 

PaT<.  PI3. 

There  are  also  several  oxychlorides,  sulphochlo- 
rides,  oxybromides,  etc.,  having  formulae  as  follows: 

POC13.  POBr8.  PSC13,  etc. 


PHOSPHORUS. 


157 


Some  of  these  bodies  are  very  useful  in  the  prepara- 
tion of  many  organic  compounds. 

In  the  light  of  the  foregoing  formulae  we  are  at 
once  led  to  ask  a  very  serious  question  as  to  the 
valency  of  phosphorus.  In  PH3  it  is  apparently 
trivalent,  and  also  in  PC13,  PBr8,  and  PI8 ;  but,  in 
the  higher  compounds,  PF5,  PC15,  and  PBr5,  it  seems 
to  have  a  valency  of  five.  Which  is  the  true  val- 
ency, or  are  both  equally  correct  ? 

A  complete  answer  to  this  question  would  in- 
volve elaborate  discussions  entirely  beyond  the 
scope  of  this  book.  Suffice  it  to  say  that  most 
chemists  regard  valency  as  a  variable  property  of 
the  elements,  and  that  this  variability  is  well  illus- 
trated by  phosphorus,  nitrogen,  and  sulphur.  Hy- 
drogen and  carbon  seldom,  if  ever,  vary  in  valency, 
but  the  elements  of  the  chlorine  group  seem  to 
change  occasionally.  In  NH4C1,  N2O5,  etc.,  nitro- 
gen is  regarded  as  quinquivalent ;  in  SOS,  the  val- 
ency of  sulphur  seems  to  be  six ;  in  C12O3  and  I2O5, 
chlorine  and  iodine  exhibit  valencies  of  three  and 
five  respectively.  In  general,  the  elements  may  be 
divided  into  two  great  classes:  one  having  valen- 
cies represented  always  by  even  numbers,  as  2,  4, 
6;  the  other  running  in  odd  numbers,  as  I,  3,  5, 
etc.  The  even  class  are  called  artiads,  the  odd 
elements  are  called  perissads.  This  division  is,  how- 
ever, largely  artificial,  and  represents  no  genuine 
law.  To  the  rule  there  are  several  striking  excep- 
tions. 

Some  of  the  phosphorus  compounds  cited  above 
may  be  assigned  structural  formulae  agreeing  with 
a  valency  for  the  element  of  either  three  or  five. 
For  example,  P2O5  may  be  written  either 


158  INORGANIC  CHEMISTRY. 

Ill  V 

ixp_O-P^'  or  O=P-O^P=O 

Ox  XO  VOX 

and  POC13  may  be  represented  by  either 

III  V 

?  /c. 

P-O-Cl  or  O-P-C1 

Cl  "Cl 

The  aim  of  the  chemist  always  is  to  select  that 
formula  from  among  the  possible  formulas  which 
shall  best  indicate  the  relations  of  each  compound 
to  the  other  compounds  which  may  be  derivable 
from  it.*  In  many  cases  a  careful  consideration  of 
structural  formulas  has  led  to  important  discoveries. 

*  The  subject  of  variable  valency  is  well  discussed  in  Wurtz's 
"  Atomic  Theory,"  Remsen's  "  Theoretical  Chemistry,"  and  Cooke's 
"  Chemical  Philosophy." 


CHAPTER   XVIII. 

ARSENIC,   BORON,   AND   SILICON. 

ARSENIC,  which  is  sometimes  classed  as  a  metal, 
occurs  in  the  mineral  kingdom  under  a  great  vari- 
ety of  circumstances.  The  free  element,  its  two  sul- 
phides, several  arsenides,  and  a  number  of  arsenates- 
are  common  mineral  species ;  but,  for  commercial 
purposes,  it  is  chiefly  obtained  from  arsenopyrite,  a 
sulphide  of  arsenic  and  iron.  This  mineral,  finely 
powdered,  is  heated  in  long  earthen  tubes ;  when 
arsenic,  being  volatile,  sublimes,  and  is  collected  in 
the  form  of  a  brilliant,  steel-gray,  brittle,  seemingly 
metallic  mass. 

Thus  prepared,  arsenic  has  a  specific  gravity  of 
5.7.  There  is  also  a  black  allotropic  modification, 
of  which  the  specific  gravity  is  only  4.71.  When 
heated  under  ordinary  circumstances,  it  vaporizes 
without  first  melting ;  but,  in  a  closed  vessel,  under 
pressure,  it  may  be  fused.  The  density  of  the  va- 
por is  150,  although  the  atomic  weight  of  arsenic  is 
only  75.  Hence  the  molecule  of  the  free  element 
is  As4,  and  similar  in  structure  to  the  molecule  of 
phosphorus.  The  odor  of  the  vapor  resembles  that 
of  garlic ;  and  its  development  before  the  blow-pipe 
flame  gives  us  an  easy  means  of  detecting  arsenic  in 
minerals.  A  very  impure  arsenic  is  sometimes  sold 


i6o 


INORGANIC  CHEMISTRY. 


as  a  fly-poison,  under  the  incorrect  name  of  "  co- 
balt " ;  but  the  only  important  use  of  the  element  is 
for  hardening  lead  shot. 

In  their  chemical  relations  the  compounds  of 
arsenic  closely  resemble  those  of  phosphorus.  They 
are  also  in  many  respects  quite  similar  to  the  corre- 
sponding compounds  of  nitrogen.  This  is  shown  in 
the  following  formulae : 


NH3 

PH3 

AsH3 

N203 

P203 

As2O3 

N206 

P206 

As2O6 

HNO8 

HPO« 

H3PO4 

HaAsO4 

NC13 

PC1S 

AsCls,  etc. 

Like  phosphorus,  arsenic  has  a  valency  of  either 
three  or  five. 

Arseniuretted  hydrogen  or  arsine,  AsH3,  is  a 
colorless  gas  of  terribly  poisonous  character.  Its 
discoverer,  Gehlen,  accidentally  inhaled,  a  single 
bubble  of  the  pure  compound,  and  died  in  conse- 
quence. It  is  easily  inflammable,  depositing  arsenic 
upon  any  cold  substance  which  may  be  inserted  in 
its  flame ;  and  this  fact  is  always  applied  in  the  de- 
tection of  arsenic. 

EXPERIMENT  77. — Generate  hydrogen  as  in  Ex- 
periment 7  ;  and,  observing  the  necessary  precau- 
tions, kindle  the  stream  of  gas  issuing  at  the  jet. 
Now  pour  into  the  generating-flask,  through  the 
thistle-tube,  a  few  drops  of  a  solution  of  any  com- 
pound of  arsenic.  Hold  a  piece  of  cold  porcelain 
against  the  flame,  and  a  black,  mirror-like  stain  of 
metallic  arsenic  will  be  deposited  upon  it.  This 


ARSENIC,  BORON,  AND  SILICON.  161 

stain  will  be  volatile,  and  may  be  driven  away  by 
too  much  heat.  Antimony  compounds  will  give  a 
similar  reaction,  owing  to  the  formation  of  SbH3 ; 
but  the  arsenic  stain  is  soluble  in  a  solution  of  so- 
dium hypochlorite,  whereas  the  antimony  stain  is 
not.  This  test  is  known  as  Marsh's  test  for  ar- 
senic. 

There  are  two  oxides  of  arsenic,  As2O3  and 
As2O5.  The  first  of  these,  arsenic  trioxide,  is  the 
common  white  arsenic  of  commerce,  well  known  on 
account  of  its  poisonous  properties.  It  is  formed 
whenever  arsenic  is  burned  in  the  air;  but  it  is 
usually  manufactured  on  a  large  scale  by  roasting 
arsenopyrite,  FeSAs.  It  is  a  white  solid,  which  is 
volatile  at  about  220°  C.,  giving  a  colorless  and 
odorless  vapor.  It  occurs  in  two  different  modifi- 
cations— one  crystalline,  the  other  amorphous;  the 
latter  is  the  commercial  form  of  the  compound, 
and  usually  is  found  in  lumps  which  curiously  re- 
semble porcelain.  It  is  slightly  soluble  in  water, 
forming  probably  arsenious  acid,  H3AsO3.  From 
this  acid,  many  arsenites  are  derived,  and  some  of 
them  have  practical  importance.  Sodium  arsenite 
is  used  as  a  mordant  in  calico-printing ;  and  a  dou- 
ble salt  of  copper  arsenite  and  copper  acetate  is 
known  commonly  as  Paris-green.  This  brilliant  pig- 
ment is  used  extensively  for  coloring  wall-papers, 
although  the  paper  so  tinted  is  certainly  unwhole- 
some. Whenever  a  sample  of  wall-paper  is  changed 
from  green  to  blue  by  a  drop  of  ammonia-water, 
or,  when  burned,  gives  a  green  tinge  to  the  flame, 
the  presence  of  an  arsenic  green  may  safely  be  in- 
ferred. The  test  is  really  a  test  for  copper ;  but 
nearly  all  green  pigments  containing  copper  con- 


1 62  INORGANIC  CHEMISTRY. 

tain  arsenic  as  well.*  Paris-green  is  also  used  in 
enormous  quantities  for  the  destruction  of  the  Colo- 
rado potato-beetle.  Inasmuch  as  it  is  violently  poi- 
sonous, it  should  be  handled  with  extreme  care. 
Arsenic  trioxide  itself  is  used  in  the  preparation  of 
the  foregoing  compounds,  in  glass-making,  and  in 
the  manufacture  of  aniline  red.  When  the  last- 
named  color  is  carelessly  made,  it  is  apt  to  retain  in- 
jurious traces  of  arsenic.  In  cases  of  arsenical  poi- 
soning the  best  antidotes  are  freshly  precipitated 
ferric  hydroxide  and  caustic  magnesia.  These  sub- 
stances unite  with  arsenious  acid  to  form  insoluble 
arsenites,  and  thus  prevent  its  absorption  by  the 
system.  An  emetic  is  subsequently  used  to  remove 
the  poison  from  the  stomach. 

Arsenic  pentoxide,  As2O5,  is  a  white  powder  pre- 
pared by  oxidizing  the  trioxide  with  nitric  acid. 
It  unites  with  water  to  form  orthoarsenic  acid, 
H3AsO4,  which  is  strictly  analogous  to  orthophos- 
phoric  acid,  H3PO4,  and  yields  similar  salts.  No 
acids  of  arsenic  corresponding  to  pyrophosphoric 
and  metaphosphoric  acids  have  yet  been  obtained  ; 
but  pyroarsenates  and  metarsenates,  resembling 
the  pyrophosphates  and  metaphosphates,  are  well 
known. 

The  fluoride,  chloride,  and  bromide  of  arsenic, 
AsF3,  AsCl3,  and  AsBr8,  are  all  volatile  liquids  ;  the 
iodide,  AsI3,  is  a  solid  compound.  There  are  three 
sulphides  of  arsenic,  As2S2,  As2S3,  and  AsgSg.  The 
first  is  a  brilliant  red  mineral,  called  realgar ;  and 
the  second,  which  is  also  a  natural  mineral,  is  the 

*  Brunswick-green,  an  oxychloride  of  copper,  is  the  most  important 
exception  to  this  statement.  When  doubt  arises  as  to  the  presence  of 
arsenic,  use  Marsh's  test  for  verification. 


ARSENIC,  BORON,  AND  SILICON.  ^3 

golden-yellow  orpiment.  Both  were  formerly  much 
used  as  pigments.  The  trisulphide  may  be  easily 
produced  artificially  by  adding  a  little  hydrochloric 
acid  to  a  solution  of  the  trioxide,  and  passing  in  a 
stream  of  sulphuretted  hydrogen.  It  forms  a  brill- 
iant yellow  precipitate.  The  pentasulphide  is  also 
yellow,  and  is  best  known  in  combination  with  other 
sulphides.  For  example,  corresponding  to  sodium 
arsenate,  Na3AsO4,  we  have  sodium  sulpharsenate, 
Na3AsS4.  The  latter  is  related  to  arsenic  pentasul- 
phide in  the  same  way  that  the  former  is  related  to 
arsenic  pentoxide.  Many  similar  double  sulphides, 
called  by  the  general  name  of  sulpho-salts,  are  well 
known. 

BORON,  atomic  weight  11,  is  a  trivalent  element 
which  occurs  as  a  constituent  of  many  minerals.  It 
is  chiefly  found,  however,  in  boric  (or  boracic) 
acid,  H8BO3,  and  borax,  an  acid  borate  of  sodium. 
The  element  itself  exists  in  two  modifications ;  the 
one  a  dark-brown  powder,  the  other  a  crystalline 
variety.  In  the  latter  form,  which  is  never  quite 
pure,  boron  has  a  specific  gravity  of  2.68,  is  infus- 
ible, and  is  nearly  as  hard  as  diamond.  The  crys- 
tals are  square  octahedra. 

The  compounds  of  boron  are  all  formed  upon  a 
simple  trivalent  type  ;  as,  for  example,  the  fluoride, 
BF3,  and  the  chloride,  BC13.  The  former  is  a  color- 
less gas,  the  latter  is  a  volatile  liquid.  The  hydride, 
BH3,  is  also  gaseous,  and  resembles  NH3,  PH3,  and 
AsH3  in  structure.  From  boron  trioxide,  B2O3,  by 
union  with  water,  three  acids  are  derived,  as  follows: 

B2O3  +  HaO  =  2HBO2,      metaboric  acid. 
2B2O3  +  H2O  =  H2B4O7,     pyroboric     " 
B2O3  +  3H2O  =  2H3BO3,  orthoboric   " 


1 64 


INORGANIC  CHEMISTRY. 


Orthoboric  acid, 
B(OH)8,  is  chief- 
ly  obtained  from 
a  volcanic  region 
in  Tuscany.  Jets 
of  steam,  called 
suffioni,  there  is- 
sue from  crevices 
in  a  mountain- 
side, bringing  bor- 
ic acid  with  them. 
A  tank  of  mason- 
ry is  built  around 
each  jet,  and  filled 
with  cold  spring- 
water.  This  con- 
denses the  boric 
acid,  and  then 
flows  to  a  lower 
tank  in  which 
more  acid  is  re- 
ceived, and  so  on 
down  to  the  foot 
of  the  mountain 
(Fig.  38).  At  the 
bottom  the  water 
is  evaporated  in 
leaden  pans,  and 
the  acid  is  deposi- 
ted in  white,  shin- 
ing, crystalline 
scales,  which  feel 
something  like  pa- 
raffin or  sperma- 


ARSENIC,  BORON,  AND  SILICON.  165 

ceti.  It  is  used  for  the  manufacture  of  borax,  or  so- 
dium pyroborate,  Na2B4O7ioH2O. 

Borax  is  by  far  the  most  important  compound 
of  boron.  It  is  not  only  made  from  boric  acid,  but 
it  is  also  found  in  great  quantities  in  the  water  of 
certain  saline  lagoons  in  Thibet,  and  in  the  Borax 
Lake  of  California.  It  has  a  feebly  alkaline  reaction, 
and  is  used  to  some  extent  in  the  household  for 
laundry  purposes,  and  for  driving  away  water-bugs. 
Its  important  uses,  however,  are  due  to  the  power 
which  it  possesses  of  dissolving,  when  in  the  fused 
state,  many  metallic  oxides.  It  serves  as  a  flux  in 
metallurgical  operations,  and  for  cleansing  metallic 
surfaces  which  are  to  be  brazed  together.  It  is 
also  very  largely  employed  in  making  colored  glazes 
and  enamels  for  pottery  and  porcelain.  Its  use  in 
this  direction  is  indicated  on  a  small  scale  by  its 
applications  to  blow-pipe  analysis.  Make  a  small 
loop  on  the  end  of  a  platinum  wire,  and  fuse  in  it 
enough  borax  to  make  a  little,  glassy  bead.  Add 
to  this  a  trace  of  any  manganese  compound,  and 
heat  before  the  blow-pipe,  and  it  will  acquire  an 
amethystine  tinge ;  cobalt  compounds  will  yield  a 
blue  color,  chromium  compounds  an  emerald-green, 
and  so  on.  Each  color  gives  a  characteristic  test 
for  the  metal  whose  compounds  produce  it. 

The  ten  molecules  of  water  contained  in  borax 
are  called  water  of  crystallization.  Water  so  com- 
bined forms  an  essential  part  of  very  many  crys- 
tallized salts,  and  is  easily  expelled  by  heating. 
When  borax  is  fused  it  first  melts  in  its  own  water 
of  crystallization ;  and  when  the  latter  is  wholly 
expelled,  Na2B4O7  remains  behind.  This  anhydrous 
borax,  on  account  of  its  glassy  appearance,  is  often 


1 66  INORGANIC  CHEMISTRY. 

called  "  glass  of  borax."  When  a  solution  of  borax 
is  mixed  with  strong  sulphuric  acid,  crystalline 
scales  of  boric  acid  are  deposited  upon  cooling. 

EXPERIMENT  78. — Dissolve  a  few  crystals  of 
borax  in  the  least  possible  quantity  of  water,  and 
add  to  the  solution  an  equal  bulk  of  strong  sul- 
phuric acid.  Allow  the  mixture  to  cool,  and  note 
the  formation  of  boric  acid.  Transfer  the  whole  to 
a  shallow  porcelain  or  earthen  dish,  cover  it  with  a 
layer  of  strong  alcohol,  and  ignite.  The  alcohol 
will  burn  with  a  flame  which  is  distinctly  greenish, 
especially  upon  the  edges.  By  the  production  of 
this  green  flame  boric  acid  is  easily  detected  analyt- 
ically. 

But  one  more  non-metal  remains  to  be  con- 
sidered ;  namely,  SILICON.*  This  element,  after 
oxygen,  is  the  most  important  ingredient  of  the 
earth's  crust,  and  enters  largely  into  the  composi- 
tion of  all  the  commoner  rocks  except  dolomite  and 
limestone.  Granite,  slate,  clay,  and  sandstone  are 
all  compounds  of  silicon. 

The  element  itself  has  an  atomic  weight  of  28, 
and  is,  like  carbon,  quadrivalent.  It  is  prepared  by 
heating  together  metallic  potassium  and  potassium 
silicofluoride,  K2SiF6 ;  and,  like  carbon,  may  be  ob- 
tained in  three  different  modifications.  Of  these, 
one  is  an  amorphous,  dark-brown  powder ;  the  sec- 
ond forms  hexagonal  plates  resembling  graphite ; 
and  the  third  crystallizes  in  octahedrons.  It  fuses 
at  very  high  temperatures,  and  is  insoluble  in  all 
acids  except  hydrofluoric.  It  has  no  practical  im- 
portance. 

The  compounds  of  silicon   are  numerous  and 

*  Sometimes  called  silicium. 


ARSENIC,   BORON,  AND   SILICON.  167 

complicated.  With  hydrogen  it  forms  a  colorless, 
inflammable  gas,  SiH4 ;  with  chlorine,  bromine,  and 
iodine  it  yields  the  compounds  SiCl4,  SiBr4,  and 
SiI4.  The  compounds  SiCl3Br,  Si2Cl6,  Si2Br6,  and 
Si2I6  are  also  known.  Silicon-chloroform,  SiHCl3, 
is  interesting  on  account  of  its  close  similarity  to 
ordinary  chloroform,  CHC13.  There  are  several 
series  of  silicon  compounds  which  resemble  in 
chemical  structure  the  organic  compounds  of  car- 
bon. 

Silicon  fluoride,  SiF4,  is  a  colorless,  corrosive 
gas  which  is  produced  whenever  hydrofluoric  acid 
acts  upon  other  silicon  compounds.  The  corrosion 
of  glass  by  hydrofluoric  acid  is  due  to  the  forma- 
tion of  this  fluoride.  It  is  usually  prepared  by  mix- 
ing powdered  fluor-spar,  CaF2,  with  fine  sand,  and 
heating  the  mixture  in  a  glass  flask  with  strong 
sulphuric  acid.  If  the  gas  is  passed  into  water,  a 
complex  reaction  ensues ;  a  jelly-like  mass  of  silicic 
acid  is  deposited,  and  a  new  acid,  hydrofluosilicic 
acid,  H2SiF6,  remains  in  solution.  This  acid  is  much 
used  as  a  test  reagent  in  chemical  analysis.  From 
it,  by  replacement  of  hydrogen,  a  large  series  of 
salts  may  be  derived. 

It  is  in  its  oxygen  compounds,  however,  that 
silicon  is  of  the  greatest  importance.  It  forms  one 
well-defined  oxide,  SiO2,  analogous  to  CO2 ;  and 
this  oxide  is  not  only  found  by  itself  in  nature,  but 
combined  in  a  vast  number  of  minerals.  It  also 
occurs  in  the  vegetable  kingdom,  giving  strength 
and  stiffness  to  the  stems  of  many  plants.  The 
shiny  surfaces  of  grass-stems,  of  rattan,  and  of  the 
scouring  rush,  are  especially  rich  in  silicon  dioxide 
or  silica. 


1 68  INORGANIC  CHEMISTRY. 

In  its  purest  form  silica  crystallizes  in  six-sided 
prisms,  and  is  called  quartz  or  rock-crystal  (Fig. 
39).  The  crystals  are  often  very  large  and  very 
limpid;  and  serve,  when  properly  cut,  for  making 


FIG.  39. — Group  of  Quartz  Crystals. 

spectacle-lenses,  or  as  substitutes  for  the  diamond. 
They  are  infusible,  except  before  the  oxyhydrogen 
blow-pipe,  and  are  hard  enough  to  scratch  glass. 
Frequently  quartz  is  colored  by  impurities,  and 
then  is  known  by  a  variety  of  special  names,  such 
as  rose  quartz,  smoky  quartz,  etc.  Yellow  quartz 
is  called  false  topaz ;  and  the  violet-colored  variety 
is  the  well-known  gem  amethyst.  Chalcedony, 
onyx,  jasper,  carnelian,  agate,  and  flint,  are  merely 
varieties  of  quartz ;  sand  and  sandstone  are  the 
same  substance,  more  or  less  impure.  Perfectly 
white  sand  is  nearly  pure  silica ;  the  yellowish  and 
reddish  kinds  owe  their  color  to  oxide  of  iron. 
Opal  is  an  amorphous  silica,  containing  a  little 
water. 

Silicon    dioxide    is    insoluble    in  water,  and  is 
attacked   by  no   acid   except   hydrofluoric.     Very 


ARSENIC,  BORON,   AND  SILICON.  169 

strong  and  hot  alkaline  solutions  dissolve  it  slightly, 
forming  silicates  ;  but  the  latter  compounds  are  best 
prepared  by  fusing  sand  with  sodium  or  potassium 
carbonate.  If  the  sand  is  not  in  excess,  the  fused 
mass  will  dissolve  in  water,  yielding  a  solution  of 
the  alkaline  silicate.  These  silicates  of  sodium  and 
potassium  are  known  commonly  under  the  name  of 
water-glass,  and  have  various  uses.  They  serve  to 
harden  building-stones,  and  are  used  in  making  arti- 
ficial stone  ;  they  are  introduced  into  certain  kinds 
of  soap,  and  they  are  applied  to  mordanted  calico 
previous  to  dyeing.  They  vary  in  composition ; 
but  in  general  a  silicate  may  be  compared  with  the 
corresponding  carbonate,  so  that  K2SiO3  is  similar 
in  structure  to  K2CO3.  Most  of  the  silicates,  ex- 
cept those  just  mentioned,  are  insoluble ;  and  the 
majority  of  those  known  occur  as  natural  minerals. 
Feldspar,  hornblende,  mica,  etc.,  are  common  exam- 
ples; and  garnet,  emerald,  topaz,  and  chrysolite 
are  well-known  gems.  Granite,  syenite,  trap,  and 
slate  are  mixtures  of  silicates,  some  of  which  are 
exceedingly  complicated  in  their  composition.  The 
natural  silicates  are  best  described  in  the  larger 
treatises  on  mineralogy. 

Glass,  porcelain,  and  pottery  are  artificial  mix- 
tures of  silicates.  Porcelain  and  pottery,  in  general 
terms,  are  more  or  less  impure  silicates  of  alumi- 
num, and  are  infusible.  Crown  or  window  glass  is 
a  silicate  of  calcium  and  sodium  ;  Bohemian  glass  is 
a  silicate  of  calcium  and  potassium  ;  flint  or  crys- 
tal glass  is  a  silicate  of  potassium  and  lead.  Green 
bottle-glass  is  like  window-glass,  except  that  it  con- 
tains silicates  of  iron  derived  from  the  cheap  and 
impure  materials  of  which  it  is  made.  Other  kinds 


i;0  INORGANIC  CHEMISTRY. 

of  glass  are  also  known,  containing  still  other  bases, 
but  they  are  unimportant.* 

If  hydrochloric  acid  be  added  to  a  strong  solu- 
tion of  water-glass,  a  jelly-like  mass  of  silicic  acid 
or  silicic  hydrate  will  separate  out.  To  this  mass 
the  formula  Si(OH)4,  which  represents  ortho-silicic 
acid,  is  usually  assigned ;  but  it  rapidly  loses  wa- 
ter and  becomes  converted  into  meta-silicic  acid, 
H2SiO3.  If  the  solution  of  water-glass  is  sufficiently 
dilute,  no  separation  of  silicic  acid  will  occur,  but 
all  will  remain  dissolved.  Place  such  a  solution  in 
a  vessel  made  by  tying  a  piece  of  bladder  or  parch- 
ment-paper tightly  over  the  bottom  of  a  broad 
wooden  hoop,  and  partially  immerse  the  latter  in  a 
larger  vessel  of  water  for  several  days.  The  hydro- 
chloric acid  and  the  alkaline  chloride  will  slowly 
diffuse  through  the  bladder  into  the  water,  and  in 
the  hoop  a  clear,  tasteless  solution  of  silicic  acid  will 
remain.  This,  upon  long  standing,  will  solidify  to 
a  jelly.  We  have,  then,  two  modifications  of  silicic 
acid — one  soluble,  the  other  insoluble — and  the 
former  is  found  in  small  quantities  in  many  natural 
waters.  The  geysers  of  Iceland  and  of  the  Yel- 
lowstone Park  contain  it  notably,  and  incrustations 
of  silicon  dioxide  are  deposited  around  their  edges. 
The  process  by  which  the  foregoing  solution  of 
silicic  acid  was  obtained  is  called  dialysis.  The  hoop 
and  membrane  constitute  a  dialyzer.  Through  such 
a  membrane  crystallizable  bodies,  like  salt,  sugar, 
etc.,  diffuse  easily,  while  non-crystallizable  bodies, 

*  The  chemistry  of  glass  and  porcelain  may  be  read  up  to  advan- 
tage in  Roscoe  and  Schorlemmer's  "  Treatise  on  Chemistry,"  vol.  ii, 
part  i,  pp.  462-498  ;  also  in  Wagner's  *•  Chemical  Technology,"  pp. 
268-321. 


ARSENIC,   BORON,  AND  SILICON.  171 

like  jellies,  gum,  glue,  albumen,  etc.,  can  not  pass 
at  all.  These  two  classes  of  bodies  are  termed,  re- 
spectively, crystalloids  and  colloids ;  and  when  they 
occur  in  mixture  they  may  be  easily  separated  by 
dialysis. 


CHAPTER  XIX. 

INTRODUCTORY   TO   THE   METALS. 

OF  the  seventy  elements  now  known,  fifteen 
have  been  described  as  non-metallic  ;  the  remaining 
fifty-two  being  reckoned  as  metals.  Of  these,  some, 
like  iron,  copper,  and  lead,  are  familiar  to  every- 
body ;  while  others,  such  as  sodium  and  calcium, 
are  somewhat  outside  of  ordinary  experience. 

Between  the  metals  and  the  non-metals  no  sharp 
line  can  be  drawn.  Neither  group  of  elements  can 
be  rigidly  defined,  for  they  shade  off  gradually  into 
each  other.  For  example,  arsenic  and  tellurium  are 
sometimes  called  metallic,  and  at  other  times  non- 
metallic  ;  and  with  good  reasons  either  way.  The 
classification  is  merely  one  of  convenience. 

In  general,,  however,  the  metals  are  distinguished 
by  certain  properties  ;  one  of  the  most  noteworthy 
being  the  power  of  reflecting  light  in  such  a  way  as 
to  produce  the  brilliant  metallic  luster.  This  is  best 
seen  on  freshly-cut  or  scraped  metallic  surfaces  be- 
fore any  film  of  rust  or  tarnish  has  had  time  to  form. 
This  property  is  shared  by  two  or  three  non-metals, 
and  by  many  compounds.  * 

In  color,  nearly  all  the  metals  are  whitish  or 
grayish,  like  tin  and  silver.  Calcium,  strontium,  and 
gold,  which  are  yellow,  and  copper,  which  is  dull 


INTRODUCTORY   TO    THE  METALS. 


173 


red,  are  the  only  distinct  exceptions.  All  are 
opaque,  except  occasionally  in  very  thin  layers. 
For  example,  gold-leaf  transmits  a  little  light  of  a 
greenish  tinge. 

Most  of  the  metals  are  malleable  and  ductile ; 
that  is,  they  may  be  hammered  into  leaves  and 
drawn  into  wire.  Antimony  and  bismuth,  how- 
ever, are  brittle,  and  may  be  pulverized  in  a  mor- 
tar. In  hardness  they  range  from  liquid  mercury 
and  soft  lead  up  to  iridium,  which  will  scratch  the 
hardest  steel.  In  general,  as  compared  with  the 
non-metals,  they  are  good  conductors  of  heat  and 
electricity. 

In  fusibility  and  specific  gravity  the  metals  dif- 
fer widely.  Mercury  is  liquid  at  all  temperatures 
above  —39*5°  C.,  while  platinum  and  some  allied 
metals  fuse  only  in  the  most  intense  heat  of  the 
electric  arc  or  the  oxyhydrogen  blow-pipe.  In 
lithium  we  have  the  lightest  solid  known,  and  in 
osmium  the  heaviest.  The  subjoined  table  of  spe- 
cific gravity  and  melting-point  will  be  found  useful 
for  reference : 

Melting-Point  and  Specific  Gravity  of  some  Metals. 


NAME. 

Melting- 
point. 

Specific 
gravity. 

NAME. 

Melting- 
point. 

Specific 
gravity. 

Aluminum  
Arsenic  .... 

850° 

2.583 
e  727 

Columbium  .... 
Copper           % 

IOQ1° 

7.06 
8.04.1: 

Antimony  

450° 

J  '    ' 
6.7OO 

Didymium  

6.S  44 

Barium.   .  .  . 

•3  71: 

Gallium 

10-  is0 

C.OA 

Bismuth  

260 

J'l  3 

0.821 

Glucinum  

1.64 

Cadmium. 

3M° 

867 

Gold 

1200° 

10.208 

Caesium  

065° 

1.88? 

Indium  

176° 

7.421 

Calcium 

i  t?8d 

Iridium. 

IQSO0 

22  421 

Cerium  .   ... 

6.728 

Iron  

ivy^VX 
l800° 

7.8 

Chromium  
Cobalt  . 

1800° 

8.QS7 

Lanthanum  .... 
Lead.. 

112° 

6.163 

II.W 

174 


INORGANIC  CHEMISTRY. 


NAME. 

Melting- 
point. 

Specific 
gravity. 

NAME. 

Melting- 
point. 

Specific 
gravity. 

Lithium  

1  80° 

0.585 

Silver  

IO4.O0 

IO.5I2 

Magnesium 

750° 

1.75 

Sodium  . 

05.6° 

O.Q74. 

Manganese  

1000° 

8.013 

Strontium  

vx.y/ij. 

2.58 

Mercury  

20.44° 

J 

1^.506 

Tantalum  . 

1078 

Molybdenum  .  .  . 

8.60 

Tellurium  . 

4.00° 

6.25 

Nickel  ... 

l6oo° 

8  ooo 

Thallium 

200° 

1  1  QI 

Osmium  

22.4.77 

Thorium  . 

1  1.2^ 

Palladium  

I  500° 

I2.O 

Tin  

215° 

7.3 

Platinum  

1770 

21   5O4. 

Tungsten 

'  •* 

1  0  26  1 

Potassium  

62.5° 

0.871; 

Uranium  

18685 

Rhodium  

12  I 

Vanadium 

r  r 

Rubidium  

38.  5° 

1.  52 

Zinc  

421° 

7SiS 

Ruthenium  .  . 

J~, 
12  2OI 

Zirconium 

A    1C 

T"1  5 

The  more  important  differences  between  the 
metals  and  the  non-metals,  however,  are  not  physi- 
cal, but  chemical.  In  general  terms  the  oxides  of 
the  non-metals  unite  with  water  to  form  acids,  while 
those  of  the  metals  produce  bases.  The  only  acid- 
forming  metallic  oxides  are  those  which  contain 
unusually  large  proportions  of  oxygen.  In  order 
to  make  this  matter  clear,  we  must  briefly  consider 
the  subject  of  electro-chemistry. 

Whenever  a  current  of  electricity  is  passed 
through  a  compound  liquid,  the  latter  will  be  de- 
composed into  two  parts.  In  Experiment  19,  water 
was  so  decomposed  into  oxygen  and  hydrogen, 
which  were  collected  in  separate  tubes  placed  over 
the  "poles,"  "terminals,"  or  "electrodes,"  of  the 
galvanic  battery.  This  method  of  decomposition 
is  called  electrolysis,  and  the  liquid  which  is  analyzed 
is  known  as  the  electrolyte. 

In  the  battery  itself,  with  which  we  effect  elec- 
trolysis, chemical  action  is  taking  place.  In  its 
simplest  form  the  galvanic  battery  consists  of  a 


INTRODUCTORY   TO    THE  METALS.         175 

plate  of  zinc  and  a  plate  of  copper  immersed  in 
dilute  sulphuric  acid,  which  acts  unequally  upon 
the  two  metals.  Whenever  we  have  such  an  in- 
equality of  action  between  two  conductors  in  a 
conducting  liquid,  an  electrical  difference  is  pro- 
duced which  may  be  utilized  as  an  electric  current. 
The  greater  the  inequality  of  action  the  stronger 
the  current  will  be.  In  all  cases  the  plate  which  is 
most  attacked  will  be  electro-positive;  the  other 
becoming  at  the  same  time  electro-negative.*  In 
the  forms  of  battery  most  generally  in  use,  zinc  is 
the  electro-positive  element ;  the  material  of  the 
other  plate  being  varied.  It  would  be  possible, 
however,  to  use  with  zinc  a  metal  which  should  be 
more  vigorously  attacked  by  sulphuric  acid,  and  in 
that  case  the  zinc  would  become  electro-negative. 
When  the  terminal  wires  of  a  cell  or  battery  are 
connected,  the  current  flows  from  the  positive  ele- 
ment through  the  exciting  liquid  to  the  negative 
element,  and  then  through  the  wires  back  to  the 
positive  plate  to  complete  the  circuit. 

Now,  when  electrolysis  takes  place,  as  in  the 
decomposition  of  water,  we  have  the  two  terminal 
wires  of  the  battery  dipping  separately  into  the 
liquid.  The  latter  is  separated  by  the  current  into 
two  parts,  one  of  which  goes  to  one  pole  of  the 
battery,  and  the  other  to  the  other  pole.  The  part 
which  appears  at  the  pole  connected  with  the  zinc 
plate,  is  electro-positive ;  the  part  which  appears  at 
the  other  pole  is  electro-negative.  In  short,  all  the 
products  of  electrolysis  exhibit  electrical  polarity ; 

*  For  the  full  definition  of  these  terms,  as  well  as  for  the  descrip- 
tion of  the  different  forms  of  battery,  a  work  on  physics  must  be  con- 
sulted. 


jy6  INORGANIC  CHEMISTRY. 

so  that  one  becomes  positive  with  respect  to  the 
other.  Oxygen  is  electro-negative,  hydrogen  is 
electro-positive ;  between  the  two  there  is  a  strong 
chemical  affinity.  Between  two  electro-negative 
or  two  electro-positive  elements,  affinity  is  weak. 
Chemical  affinity,  then,  bears  a  strong  resemblance 
to  electrical  and  magnetic  attractions. 

If,  now,  we  subject  a  great  many  compounds  to 
electrolysis,  and  note  carefully  at  which  electrodes 
the  products  of  decomposition  appear,  we  shall  be 
able  to  arrange  all  the  elements  in  an  electro-chemical 
series,  as  follows.  For  present  purposes  we  may 
ignore  the  rarer  elements  and  confine  our  attention 
to  the  commoner  substances  : 

Electro-negative. 

Oxygen.  Antimony.  Nickel. 

Sulphur.  Silicon.  Iron. 

Nitrogen.  Hydrogen.  Zinc. 

Fluorine.  Gold.  Manganese. 

Chlorine.  Platinum.  Aluminum. 

Bromine.  Mercury.  Magnesium. 

Iodine.  Silver.  Calcium. 

Phosphorus.  Copper.  Strontium. 

Arsenic.  Bismuth.  Barium. 

Chromium.  Tin.  Lithium. 

Boron.  Lead.  Sodium. 

Carbon.  Cobalt.  Potassium. 

Electro-positive. 

In  this  series,  which  should  be  read  as  if  it  were 
written  in  a  single  vertical  column,  each  element  is 
negative  to  those  which  follow  it,  and  positive  to 
those  which  precede  it.  Iodine,  for  instance,  is  the 
negative  element  in  potassium  iodide,  but  positive 
in  its  oxygen  compounds.  In  general,  however, 
the  non-metallic  elements  are  strongly  electro-negative, 


INTRODUCTORY   TO    THE  METALS.         177 

while  the  metals  form  the  positive  end  of  the  chain. 
Here  we  find  the  most  essential  difference  between 
the  two  classes  of  elements.  It  must  never  be  for- 
gotten that  "  positive "  and  "  negative,"  as  here 
used,  are  only  terms  of  comparison,  and  have  no 
final  significance.  An  element  is  positive  under 
certain  conditions,  and  negative  under  others,  just 
as  a  hill  is  said  to  be  low  when  compared  with  a 
mountain,  and  high  when  contrasted  with  a  valley. 

Electrolysis  may  be  effected  upon  liquids  under 
very  varying  circumstances.  The  liquid  may  exist 
at  ordinary  temperatures  as  a  single,  definite  com- 
pound  ;  it  may  be  a  substance  kept  in  a  state  of 
fusion  at  a  high  heat ;  or  it  may  consist  of  a  salt 
dissolved  in  some  fluid  like  water.  In  the  latter 
case  the  chemical  reactions  may  become  quite  com- 
plicated, as  the  following  experiment  and  its  expla- 
nation will  show : 

EXPERIMENT  79. — Fill  a  U-tube  (Fig.  40)  with  a 


FIG.  40. — Electrolysis  of  Na2SO4. 

strong  solution  of  sodium  sulphate,  colored  with  an 
infusion  of  red  cabbage.  Into  the  solution,  at  the 
two  limbs  of  the  tube,  dip  the  terminals  of  a  small 
galvanic  battery,  and  allow  the  current  to  pass. 


i;8  INORGANIC  CHEMISTRY. 

At  the  pole  which  is  connected  with  the  zinc  of  the 
battery,  the  liquid  will  become  alkaline,  and  turn 
green ;  at  the  other  pole  free  acid  may  be  detected, 
and  the  color  remains  red.  By  electrolysis,  then,  a 
neutral  salt  dissolved  in  water  may  be  decomposed 
into  an  electro-negative  acid  and  an  electro-positive 
base.  In  the  case  under  consideration,  the  reac- 
tions are  as  follows : 

First,  the  Na2SO4  is  split  up  into  Na2  and  SO4. 
The  latter  loses  an  atom  of  oxygen,  which  is  given 
off  at  the  proper  pole,  leaving  SO3.  This  unites  at 
once  with  water  to  form  H2SO4.  At  the  other  side 
of  the  equation  the  Na2  decomposes  some  of  the 
water,  evolving  hydrogen,  and  forming  sodium 
hydroxide,  NaOH,  thus : 

Na2  +  2H2O  =  H2  +  2NaOH. 

The  latter  compound  is  a  strong  alkali,  and  readily 
reunites  with  sulphuric  acid,  as  follows : 

2NaOH  +  H2SO4  ==  Na2SO4  +  2H2O. 

Whenever  any  salt  is  electrolyzed,  the  acid  por- 
tion is  separated  as  an  electro-negative  group  of 
atoms,  and  the  basic  portion  as  an  electro-positive 
group.  The  stronger  the  base  or  the  acid,  the 
more  distinctly  marked  its  positive  or  negative 
character  will  be.  Most  bases  and  most  acids  con- 
tain hydroxyl,  HO ;  and  when  they  unite  they  do 
so  with  evolution  of  water,  as  in  the  equation  last 
given  above.  In  forming  a  neutral  salt,  all  of  the 
hydrogen  contained  in  the  hydroxyl  of  both  acid 
and  base  is  thus  removed.  An  acid  salt  retains 
part  of  the  hydrogen  of  the  acid ;  a  basic  salt  re- 
tains some  oxygen  from  the  hydroxyl  of  the  base. 


INTRODUCTORY   TO    THE  METALS.         179 

In  future  chapters  the  applications  of  electroly- 
sis to  electrotyping  and  electroplating  will  be  duly 
described.* 

The  metals,  like  the  non-metals,  are  best  classi- 
fied according  to  valency.  Thus,  sodium  and  po- 
tassium are  univalent,  calcium  and  magnesium  are 
bivalent,  gold  is  trivalent,  and  tin  is  quadrivalent. 
The  classification  is  most  instructive,  however, 
when  we  consider  all  the  elements  together,  and 
ignore  our  old  division  into  a  metallic  and  a  non- 
metallic  group.  Let  us  begin  by  arranging  some 
of  the  elements  in  the  order  of  their  atomic  weights, 
starting  with  hydrogen,  the  lowest : 

H  ='i. 

Li  =  7.    Gl  =  9.    B  =11.    C  =  12.    N=I4.       O  =16.    F  =19. 
Na=23.    Mg=24.    Al=27.    Si  =28.    P  =31.       S  =32.  Cl  =35-5- 
K   =39.    Ca=40.    80=44.    Ti=48.    V=5i.5.    Cr=52.   Mn=55. 

If,  now,  we  consider  any  horizontal  line  in  this 
table,  we  shall  see  that  it  begins  with  a  univalent 
element;  the  next  is  bivalent,  the  third  trivalent, 
the  fourth  quadrivalent,  etc.  Furthermore,  the 
elements  which  are  closely  related  to  each  other 
fall  into  the  same  vertical  column,  as  Na  and  K,  C 
and  Si,  N  and  P,  O  and  S,  F  and  Cl.  Toward  the 
left-hand  side  of  the  table  the  elements  are  strongly 
basic;  toward  the  right  they  are  distinctly  acid- 
forming  ;  in  the  middle  columns  the  electro-chemi- 
cal character  is  less  definitely  marked.  If  we  study 
the  chief  oxides  formed  by  these  elements,  some  of  the 
regularities  due  to  valency  will  become  very  clear : 

Na2O.       Mg2O2.      AlaO8.       Si2O4.       P2O6.       S2O«.       C12O7. 
KaO.         Ca2O2.       Sc2O3.       Ti2O4.      V2O6.       Cr2O8.      MnaO7. 

*  Gore's  work,  "  The  Art  of  Electro-Metallurgy,"  is  a  most  ex- 
cellent little  treatise  upon  this  theme. 


180  INORGANIC  CHEMISTRY. 

Here  the  proportion  of  oxygen  steadily  increases 
from  one  end  of  each  line  to  the  other.  Six  of  the 
formulas  have  been  doubled  in  order  to  make  this 
ratio,  which  is  only  a  ratio,  more  apparent. 

We  see,  then,  that  the  elements  vary  in  their 
chemical  relations  with  a  remarkable  regularity, 
and  that  they  seem  to  be  connected  with  each  other 
by  some  definite  law.  Were  it  not  so,  a  bivalent 
element  might  be  followed  by  one  which  was  quad- 
rivalent, and  its  next  neighbor  in  turn  might  have 
any  valency  whatever.  If  we  study  the  physical 
properties  of  the  elements,  similar  regularities  will 
confront  us,  at  every  step,  of  the  most  unmistak- 
able character.  In  brief,  it  is  now  generally  be- 
lieved by  chemists,  although  not  as  yet  fully  proved, 
that  all  the  properties  of  an  element  depend  in  some 
way  upon  its  atomic  weight.  For  example,  the 
specific  heat  of  an  element  is  inversely  proportional 
to  its  atomic  weight ;  or,  in  other  words,  all  the 
elementary  atoms  have  precisely  the  same  capacity 
for  heat.  This  point  will  be  brought  out  more 
fully  in  another  chapter. 

On  the  opposite  page  a  table  of  the  elements 
is  given,  based  upon  the  principles  developed  in  the 
preceding  paragraphs.  This  table  is  due  chiefly 
to  a  Russian  chemist,  D.  Mendelejeff,*  who  was 
able  by  means  of  it  to  predict  the  existence  of 
two  new  elements  long  before  they  were  actually 
discovered ;  namely,  gallium  and  scandium.  Wher- 
ever a  blank  occurs  in  the  table,  some  element  yet 
to  be  discovered  probably  belongs.  Such  blanks 
existed  where  gallium  and  scandium  are  now  placed  ; 

*  Similar  tables  were  independently  devised  by  Newlands  and  Lo- 
thar  Meyer. 


INTRODUCTORY   TO    THE  METALS. 


181 


G  ^ 

>l 


o  co 


HO 


w 


0          M 


s- 


So 


*  a 


offi 


4 

ii 

>., 
N 


Offi 

c5 


^ 

I! 

g 
O 


to       H 

s    1! 

u 


II  2! 


1 82  INORGANIC  CHEMISTRY. 

and  from  their  position  Mendelejeff  foretold  not 
only  their  existence,  but  also  their  leading  proper- 
ties. These  predictions  are  now  regarded  as  among 
the  most  remarkable  achievements  of  modern  sci- 
ence.* Unfortunately,  the  subject  is  not  suited  to 
thorough  treatment  in  an  elementary  text-book. 

*  For  fuller  discussions  of  Mendelejeff 's  "  Periodic  Law,"  the 
student  may  consult  Roscoe  and  Schorlemmer's  treatise,  vol.  ii,  part 
ii,  p.  506;  or  Wurtz's  "Atomic  Theory,"  p.  154. 


CHAPTER  XX. 

THE   METALS   OF  THE  ALKALIES. 

THE  metals  of  the  alkalies  are  five  in  number, 
and  form  a  very  definite  univalent  group.  They 
exhibit  a  regular  gradation  in  properties,  which  is 
well  indicated  in  the  following:  table  : 


NAME. 

Atomic 

weight. 

Specific 
gravity. 

Melting- 
point. 

Lithium, 

Li  

7-    ' 

0.585 

180.° 

Sodium, 

Na  (Natrium).     .    .  . 

27. 

O  074. 

05  6° 

Potassium, 

K  (Kalium)  

^o. 

0.875 

62.5° 

Rubidium 

Rb 

8c  5 

1  52 

l8  5° 

Caesium, 

Cs  

I?-z. 

1.885 

26  5° 

All  of  these  metals  are  silver-white,  and  soft 
enough  to  be  easily  cut  with  a  knife.  They  are  all 
readily  oxidizable — so  much  so,  that  they  have  to 
be  kept  under  naphtha  to  preserve  them  from  the 
action  of  the  air.  Thrown  upon  water,  they  decom- 
pose it,  forming  soluble  hydroxides  and  setting  hy- 
drogen free.  This  is  done  quietly  by  lithium,  very 
violently  by  caesium  ;  the  other  metals  of  the  group 
being  graded  between  these  extremes. 

EXPERIMENT  80.— Throw  into  a  vessel  of  cold 
water  a  bit  of  potassium  half  as  large  as  a  pea.  It 
will  fuse,  move  about  rapidly  on  the  surface  of  the 

9 


1 84  INORGANIC  CHEMISTRY. 

water,  and  seemingly  burst  into  violet-colored  flame. 
The  flame  is  really  due  to  the  burning  of  the  hydro- 
gen which  has  been  liberated.  The  color  is  caused 
by  the  vapor  of  the  potassium.  Sodium,  under  simi- 
lar circumstances,  will  act  in  much  the  same  way, 
only  the  action  is  not  violent  enough  for  the  hydro- 
gen to  ignite.  Thrown  on  wet  paper,  however,  so 
that  the  heat  of  action  may  be  confined  to  one  spot, 
the  hydrogen  set  free  by  the  sodium  will  kindle,  and 
burn  with  a  yellow  flame.  The  yellow  color  is  char- 
acteristic of  sodium  and  its  compounds. 

Concerning  LITHIUM,  RUBIDIUM,  and  CESIUM, 
little  need  be  said.  All  three  are  comparatively 
rare.  Lithium  compounds  are  somewhat  used  in 
medicine,  and  give  a  magnificent  red  color  to  a 
flame.  Rubidium  and  caesium  resemble  potassium 
so  closely  that  they  are  difficult  to  distinguish  from 
it.  They  were  discovered  by  spectrum  analysis, 
which  will  be  described  in  another  chapter.  The 
best  source  of  the  three  metals  is  the  rare  mineral 
lepidolite.  Csesium  is  the  most  electro-positive  ele- 
ment known.  Hence  it  has  a  very  strong  affinity 
for  electro-negative  oxygen. 

Before  the  introduction  of  systematic  names  into 
chemistry,  soda,  potash,  and  ammonia  were  known 
as  mineral  alkali,  vegetable  alkali,  and  volatile  alkali, 
respectively.  In  1807  Davy  succeeded  in  decom- 
posing soda  and  potash  by  means  of  a  powerful  elec- 
tric current,  and  in  isolating  the  metals  which  they 
contained.  Soon  afterward,  chemical  methods  of 
preparing  sodium  and  potassium  were  devised,  the 
best  one  consisting  in  heating  the  carbonates  of  the 
metals  with  charcoal  in  an  iron  retort.  The  reac- 
tion which  takes  place  is  as  follows : 


THE  METALS  OF    THE  ALKALIES.          185 

Na2CO3  +  2C  =  Na2  +  SCO. 
KaCO3  +  2C  =  Ka  +  3CO. 

The  beak  of  the  retort  dips  under  naphtha — in 
which  the  vapor  of  the  sodium  or  potassium,  as  it 
distills  over,  is  condensed.  Both  metals  are  easily 
volatilized.  As  metals  they  have  but  few  uses,  al- 
though their  compounds  are  of  the  highest  practi- 
cal importance.  Sodium  is  used  to  some  extent  in 
the  preparation  of  aluminum  and  magnesium,  and 
is  also  of  value  in  some  lines  of  chemical  research. 

SODIUM  is  one  of  the  most  abundant  of  elements. 
The  chloride  exists  in  enormous  quantities  in  sea- 
water,  in  many  salt-lakes  and  mineral  springs,  as 
rock-salt,  in  marine  plants,  and  in  the  various  ani- 
mal juices.  The  nitrate,  the  carbonate,  and  the  bo- 
rate  occur  in  large  natural  deposits  ;  cryolite,  a  flu- 
oride of  sodium  and  aluminum,  forms  an  inexhausti- 
ble bed  in  Greenland  ;  many  silicates  contain  sodi- 
um as  an  essential  ingredient. 

The  chief  commercial  source  of  sodium  com- 
pounds is  sodium  chloride,  NaCl,  or  common  salt. 
Great  beds  of  rock-salt,  which  is  often  perfectly 
transparent,  are  worked  at  Northwich  in  England, 
Wieliczka  in  Poland,  Stassfurt  in  Germany,  and 
the  Island  of  Petit  Anse  in  Louisiana.  Near  Syra- 
cuse, New  York,  Saginaw,  Michigan,  and  in  the 
Kanawha  Valley  of  West  Virginia,  salt  is  made  in 
vast  quantities  by  the  evaporation  of  natural  brines 
which  rise  through  artesian  wells  from  subterra- 
nean springs.  It  is  also  prepared  in  many  places 
from  sea-water. 

Sodium  chloride  crystallizes  in  cubes,  and  has 
a  specific  gravity  of  2.15.  As  common  salt,  and  in 
its  use  as  a  food-preservative  and  condiment,  it  is 


1 86  INORGANIC  CHEMISTRY. 

familiar  to  every  one.  It  is  also  used  in  great  quan- 
tities for  the  manufacture  of  chlorine  and  hydrochlo- 
ric acid,  as  a  fertilizer,  and  in  the  glazing  of  earthen- 
ware. 

Sodium  forms  two  oxides,  Na2O  and  Na2O2,  but 
neither  is  important.  The  hydroxide,  NaOH,  how- 
ever, is  of  great  importance.  When  sodium  is 
thrown  into  water,  this  substance,  which  is  com- 
monly called  caustic  soda,  remains  in  solution  ;  but 
practically  it  is  usually  prepared  from  the  carbon- 
ate. The  latter  is  dissolved  in  water  and  mixed 
with  milk  of  lime  ;  calcium  carbonate  is  deposited 
as  an  insoluble  white  powder,  and  caustic  soda  re- 
mains in  solution.  By  boiling  down  in  iron  pans  it 
is  obtained  as  a  white  solid,  having  a  strong  soapy 
feel,  and  acting  corrosively  upon  the  skin.  It  is 
one  of  the  strongest  alkalies.  The  reaction  which 
yields  it  may  be  written  as  follows : 

Na2CO3  +  CaH2O3  =  2NaOH  +  CaCO3. 

Caustic  soda  is  used  in  refining  fats  and  oils,  espe- 
cially cotton-seed  oil,  and  on  a  very  large  scale  in 
the  manufacture  of  soap.  Soap  is  a  compound  of 
either  alkali,  with  certain  organic  acids  which  are 
found  in  fats  and  oils.  The  soda-soaps  are  hard 
soaps,  the  potash-soaps  are  soft  soaps.  They  are 
produced  by  boiling  the  alkali  with  the  fat ;  and 
from  a  chemical  stand-point  they  are  just  as  truly 
salts  of  their  respective  acids  as  are  the  nitrates, 
sulphates,  or  chlorides.  A  hard  soap  made  from  an 
animal  fat  is  mainly  sodium  stearate,  QgH^NaC^. 

Sodium  carbonate,  NagCOg,  is  a  white  solid  hav- 
ing a  strong  alkaline  reaction.  The  base  is  so 
strong,  and  the  acid  so  weak,  that  in  this  salt  the 


THE  METALS  OF   THE  ALKALIES.          jg/ 

basic  character  predominates.  It  crystallizes  with 
ten  molecules  of  water  of  crystallization,  Na2CO3, 
ioH2O,  and  occurs  in  commerce  both  in  this  form 
and  dry.  Crystallized  sodium  carbonate,  or  "sal 
soda,"  is  the  common  washing-soda  of  the  laundries. 
The  dry  carbonate  is  used  in  preparing  other  so- 
dium compounds,  and  in  enormous  quantities  in  the 
manufacture  of  glass  and  soap.  Hence  its  prepara- 
tion constitutes  one  of  the  largest  chemical  indus- 
tries. 

Sodium  carbonate  is  commercially  manufactured 
by  several  processes ;  but  only  one,  the  process  in- 
vented by  Leblanc,  is  of  sufficient  importance  to 
warrant  description  here.*  First,  sodium  chloride 
is  treated  with  sulphuric  acid,  yielding  sodium  sul- 
phate and  hydrochloric  acid,  thus : 

2NaCl  +  HaSO4  =  2HC1  +  Na2SO4. 

The  operation  is  performed  in  a  suitable  furnace, 
about  half  a  ton  of  salt  being  treated  at  a  time; 
and  the  hydrochloric  acid  is  in  most  establishments 


FIG.  41. — Black-ash  Furnace. 

condensed  by  water  and  saved.     The  crude  sodium 
sulphate  is  technically  known  as  "  salt-cake." 

The  second  stage  of  the  manufacture  consists  in 

*  Another  process,  the  "  ammonia-soda  process,"  now  bids  fair  to 
supplant  Leblanc's  method. 


1 88  INORGANIC  CHEMISTRY. 

the  conversion  of  the  salt-cake  into  sodium  carbon- 
ate, and  is  called  the  "  black-ash  "  process.  Ten 
parts  of  salt-cake,  ten  of  limestone,  in  small  frag- 
ments, and  seven  and  a  half  of  coal,  are  heated 
together  in  a  reverberatory  furnace  until  the  mass 
fuses,  when  it  is  taken  out  to  cool.  Two  reactions 
here  take  place ;  first,  the  carbon  of  the  coal  with- 
draws oxygen  from  the  salt-cake,  leaving  sodium 

sulphide : 

Na2SO4  +  C4  =  Na2S  +  4CO. 

The  limestone  (calcium  carbonate)  next  reacts  upon 
the  sodium  sulphide,  forming  by  double  decomposi- 
tion calcium  sulphide  and  sodium  carbonate,  as  fol- 
lows: 

NaaS  +  CaCO3  =  Na2CO3  +  CaS. 

By  treating  the  black-ash  with  water,  the  sodium 
carbonate  is  dissolved  out,  and  afterward,  by  evap- 
oration, it  is  obtained  in  crystals.  These,  calcined, 
yield  the  dry  carbonate,  which  is  the  soda-ash  of 
commerce.  The  calcium  sulphide,  which  remains 
undissolved,  is  worked  over  for  the  recovery  of  the 
sulphur  which  it  contains  ;  so  that  from  first  to  last, 
during  the  entire  process,  little  or  nothing  is  lost 
or  wasted.  In  Great  Britain  alone,  at  least  half  a 
million  tons  of  common  salt  are  annually  convert- 
ed into  sodium  carbonate.  In  consequence  of  Le- 
blanc's  process  sal-soda  now  costs  less  than  one  tenth 
of  what  it  did  a  century  ago ;  and,  of  course,  glass 
and  soap  have  been  proportionally  cheapened.  Al- 
though the  whole  world  has  been  benefited  by  the 
invention,  Leblanc  himself  was  allowed  to  die  in  ab- 
ject misery. 

When  the  crystallized  sodium  carbonate  is  ex- 


THE  METALS   OF    THE  ALKALIES.          189 

posed  to  the  action  of  carbon  dioxide,  sodium 
hydrogen  carbonate,  NaHCO3,  or  "  bicarbonate  of 
soda  "  is  produced.  This  is  the  common  cooking- 
soda  of  the  household,  and  an  important  constituent 
of  all  baking-powders.  It  is  also  used  in  medi- 
cine, and  in  the  preparation  of  various  effervescent 
drinks. 

Only  a  few  other  sodium  salts  require  especial 
mention  here.  The  sulphate,  Na2SO4,  is  important 
as  salt-cake;  and,  crystallized,  as  Na2SO4,ioH2O, 
it  is  known  as  Glauber's  salts,  and  has  some  me- 
dicinal value.  The  acid  sulphate,  NaHSO4,  is  used 
in  chemical  analysis.  The  nitrate,  NaNO3,  is  found 
in  large  beds  in  Chili,  Peru,  and  Bolivia,  whence 
its  commercial  name  of  Chili  saltpeter.  It  is  used 
as  a  fertilizer,  in  the  manufacture  of  nitric  acid,  and 
for  the  preparation  of  common  saltpeter.  Sodium 
thiosulphate,  Na2S2O3,  5H2O,  has  already  been  men- 
tioned on  account  of  its  use  in  photography  ;  sodium 
hypochlorite,  NaCl2O2,  has  some  applications  as  a 
disinfectant ;  the  chlorate,  NaQO3,  is  employed  as 
an  oxidizing  agent  in  dyeing  with  aniline  black ; 
and  one  of  the  phosphates,  Na2HPO4,  i2H2O,  is  an 
important  laboratory  reagent,  and  also  of  value 
medicinally.  Borax,  Na2B4O7,  ioH2O,  and  sodium 
silicate  or  water-glass,  have  been  sufficiently  de- 
scribed in  previous  chapters. 

POTASSIUM,  although  less  widely  diffused  in  na- 
ture than  sodium,  is  still  one  of  the  most  abundant 
elements.  It  is  contained  in  most  granitic  rocks, 
whence  it  finds  its  way  into  the  soil,  from  which  it 
is  extensively  taken  up  by  growing  plants.  For- 
merly its  compounds  were  almost  exclusively  ob- 
tained from  wood-ashes,  whence  the  old  name  of 


190  INORGANIC  CHEMISTRY. 

vegetable  alkali,  as  applied  to  its  carbonate.  To- 
day, great  quantities  of  potassium  salts  are  derived 
from  the  Stassfurt  salt-beds. 

There  are  two  oxides  of  potassium,  K2O  and 
K2O4.  From  the  first,  potassium  hydroxide,  KOH, 
or  caustic  potash,  is  derived.  Practically,  however, 
this  important  compound  is  prepared  from  potas- 
sium carbonate  by  treatment  with  milk  of  lime,  just 
as  in  the  preparation  of  caustic  soda.  It  closely 
resembles  the  latter  substance,  and  is  used  for 
similar  purposes. 

Potassium  carbonate,  K2CO3,  is  the  familiar  sub- 
stance potash.  The  simplest  mode  of  preparing 
this  compound  is  to  boil  wood-ashes  with  water, 
and  afterward  to  evaporate  the  solution.  Until  a 
few  years  ago,  nearly  all  the  potash  of  commerce 
was  obtained  from  this  source ;  but  now  a  variety 
of  other  sources  are  available.  First,  potassium 
chloride  and  potassium  sulphate  are  found  in  large 
quantities  in  the  Stassfurt  salt-beds.  These  are 
treated  by  Leblanc's  process  in  just  the  same  man- 
ner as  the  corresponding  sodium  compounds,  and 
yield  potassium  carbonate  by  precisely  similar  re- 
actions. Secondly,  the  residues  left  behind  in  the 
manufacture  of  beet-root  sugar,  yield  annually  some 
thousands  of  tons  of  potash.  Thirdly,  there  is  the 
most  extraordinary  source  of  all.  Sheep,  when 
feeding,  take  up  large  quantities  of  potassium  salts 
from  the  soil.  These  are  exuded  in  the  perspira- 
tion, and  remain  adhering  to  the  wool.  When  the 
wool  is  washed  at  some  of  the  great  European 
centers  of  the  woolen  industry,  the  wash-water  is 
evaporated  to  dryness,  and  a  substance  known  as 
"  suint "  is  obtained.  This,  which  contains  the 


THE  METALS  OF   THE  ALKALIES.          191 

potassium  salts  of  certain  organic  acids,  is  heated 
in  iron  retorts,  giving  off  a  fair  quality  of  illuminat- 
ing gas.  From  the  charred  residue,  water  extracts 
potassium  carbonate.  By  this  curious  process, 
which  splendidly  illustrates  the  way  in  which 
chemistry  utilizes  seemingly  worthless  materials, 
at  least  a  thousand  tons  of  potash  are  annually 
made. 

Potassium  carbonate,  when  pure,  is  a  white  salt 
containing  no  water  of  crystallization.  It  has  a 
strong  alkaline  taste  and  reaction,  and  is  used  for 
preparing  other  potassium  compounds,  and  for  the 
manufacture  of  glass  and  soft  soap.  By  treatment 
with  carbon  dioxide,  it  yields  a  "  bicarbonate," 
KHCO3. 

Potassium  chloride,  bromide,  and  iodide,  are  all 
white  salts,  which  crystallize  in  cubes.  The  chloride 
is  chiefly  used,  as  above  indicated,  in  the  prepara- 
tion of  the  carbonate ;  the  bromide  and  iodide  are 
important  medicinally.  The  formulae,  potassium 
being  univalent,  are  naturally  KC1,  KBr,  and  KI. 

Two  other  salts  of  potassium  are  of  great  practi- 
cal importance,  the  chlorate  and  the  nitrate,  KC1OS 
and  KNO3.  The  properties  of  the  chlorate,  and  its 
uses  for  making  oxygen  and  in  pyrotechny,  have 
been  sufficiently  indicated  in  previous  chapters.  It 
is  also  used  in  medicine,  for  allaying  inflammation 
of  the  throat,  in  calico-printing,  and  in  the  manufac- 
ture of  matches. 

Potassium  nitrate,  popularly  known  as  saltpe- 
ter or  as  niter,  is  a  salt  which  crystallizes  easily  in 
long,  white  prisms.  It  occurs  naturally  in  the  soil 
in  many  tropical  countries,  especially  in  Egypt  and 
the  East  Indies,  and  is  extracted  easily  by  solution 


192 


INORGANIC  CHEMISTRY. 


in  water.  It  originates  from  the  oxidation  of  or- 
ganic matter  rich  in  nitrogen,  in  presence  of  potas- 
sium compounds.  In  Sweden  much  saltpeter  is 
prepared  artificially  by  piling  up  animal  refuse- with 
lime,  soil,  and  a  little  potash ;  and,  after  a  proper 
period  of  time,  leaching  the  mass  with  water.  It  is 
also  made  by  double  decomposition  from  the  crude 
potassium  chloride  of  Stassfurt  and  the  cheaper 
Chili  saltpeter. 

KC1  +  NaNO3  =  NaCl  +  KNO3. 

It  is  used  in  the  preservation  of  meat,  and  in  the 
manufacture  of  gunpowder. 

Gunpowder  is  a  mechanical  mixture  of  char- 
coal, sulphur,  and  saltpeter.  A  good  average  pow- 
der is  composed,  by  percentages,  as  follows : 

KNO3,    75 
C,  15 

S,  10 

IOO 

When  gunpowder  burns,  there  is  a  great  and  sud- 
den evolution  of  gas ;  and  to  the  expansion  of  the 
latter  the  force  of  explosion  is  due.  A  cubic  centi- 
metre of  powder  gives  about  280  cc.  of  gas ;  and 
the  reaction,  which  in  reality  is  very  complicated, 
is  approximately  represented  by  the  subjoined  equa- 
tion :  * 

2KN03  +  S  +  3C  =  K2S  +  N2  +  3CO2. 

The  total  explosive  force  of  a  pound  of  gunpow- 
der, expressed  in  mechanical  terms,  is  equivalent 

*  There  is  a  good  discussion  of  this  subject  in  Roscoe  and  Schor- 
lemmer's  '*  Treatise  on  Chemistry,"  vol.  ii,  part  i,  pp.  8 1-88. 


THE  METALS  OF   THE  ALKALIES.          JQJ 

to  a  power  of  lifting  a  weight  of  486  tons  one  foot 
high. 

AMMONIUM,  NH4,  is  a  compound  radicle  which 
is  most  conveniently  studied  in  connection  with  the 
alkaline  metals.  It  plays  the  part  of  a  metal,  and 
its  salts  in  many  respects  are  very  similar  to  those  of 
potassium.  When  ammonia,  NH8,  is  brought  into 
contact  with  HCl,  union  takes  place,  and  NH4C1  is 
formed.  So  also,  when  ammonia  is  passed  into  wa- 
ter, the  strongly  alkaline  solution  may  be  regarded 
as  having  the  formula  NH3,  H2O,  or  NH4OH.  In 
one  compound,  we  have  the  chloride  of  NH4,  and 
in  the  other  an  alkaline  hydroxide  similar  in  char- 
acter to  KOH  and  NaOH.  Like  the  latter  hy- 
droxides the  ammonium  hydroxide  or  caustic  am- 
monia is  capable  of  saturating  the  strongest  acids, 
and  of  forming  crystalline  salts  in  which  the  NH4 
plays  precisely  the  same  part  as  K  or  Na.  In  NH4, 
which  has  not  yet  been  obtained  by  itself,  an  atom 
of  quinquivalent  nitrogen  has  four  of  its  bonds  of 
valency  saturated ;  and  by  virtue  of  the  one  which 
remains  it  is  univalent.  For  convenience,  we  may 
treat  ammonium  as  if  it  were  really  a  metal  having 
an  atomic  weight  of  18,  and  designate  it  by  the  pro- 
visional symbol  Am. 

Most  of  the  ammonium  salts  are  prepared  by 
saturating  aqua  ammonia  with  acids ;  although  in 
practice  there  are  some  exceptions.  The  chloride, 
AmCl,  is  a  white  salt  which  occurs  in  commerce  in 
tough  fibrous  masses.  It  is  purified  by  sublimation, 
being  readily  volatile.  From  its  formula  the  den- 
sity of  its  vapor  should  be  -  -  =  26.75  ; 

whereas  experiment  gives  it  a  density  only  one  half 


194 


INORGANIC  CHEMISTRY. 


as  great.  That  is,  its  vapor  forms  four  volumes  in- 
stead of  agreeing  with  the  two-volume  law.  This 
anomaly  has  been  explained  by  showing  that  at 
high  temperatures  the  compound  NH4C1  can  not 
exist ;  but  splits  up  into  NH3  and  HC1,  each  repre- 
sented by  two  volumes.  On  cooling,  the  parts  re- 
combine,  again  forming  NH4C1.  This  splitting  up 
so  as  to  give  an  unusual  vapor-density  is  called  dis- 
sociation, and  many  examples  of  it  are  known.  The 
explanation  is  not  wholly  theoretical,  but  rests  upon 
solid  experimental  demonstrations. 

Ammonium  chloride  has  some  medicinal  use, 
is  largely  employed  in  dyeing,  and  is  a  source 
of  other  ammonium  compounds.  In  soldering  and 
tinning  it  serves  to  cleanse  the  metallic  surfaces. 
Ammonium  sulphate,  Am2SO4,  is  important  as  a  fer- 
tilizer; the  nitrate,  AmNO3,  is  used  in  making  ni- 
trous oxide  ;  and  a  phosphate  of  sodium,  hydrogen, 
and  ammonium,  NaHAmPO4, 4H2O,  microcosmic 
salt,  is  a  useful  reagent  in  blow-pipe  analysis. 

When  hydrogen  sulphide,  H2S,  is  passed  into 
aqua  ammonia,  ammonium  hydrosulphide,  AmSH, 
is  formed.  There  are  also  several  sulphides  of  am- 
monium, of  which  Am2S  is  the  most  typical.  These 
compounds  are  much  used  as  test  reagents  in  chem- 
ical analysis. 

EXPERIMENT  81. — Dissolve  in  water,  in  separate 
test-tubes,  fragments  of  zinc  sulphate,  iron  sulphate, 
copper  sulphate,  manganese  chloride,  arsenious  ox- 
ide, and  tartar  emetic.  Add  to  each  solution  a  drop 
of  ammonium  hydrosulphide,  and  note  the  color  of 
the  precipitate.  On  adding  an  excess  of  the  re- 
agent, the  arsenic  and  antimony  precipitates  will 
redissolve. 


THE  METALS  OF   THE  ALKALIES. 


195 


Ammonium  carbonate  is  another  salt  which  is 
used  in  medicine  and  as  a  reagent  in  analysis.  It 
has  a  complicated  formula,  and  occurs  in  commerce 
under  the  name  of  sal-volatile.  It  smells  strongly 
of  ammonia,  and  is  often  met  with  in  the  form  of 
"  smelling-salts/' 

From  ammonia  and  ammonium  a  number  of 
other  strong  bases  are  derived,  which  will  be  de- 
scribed in  connection  with  organic  chemistry. 


CHAPTER  XXI. 

SILVER  AND   THALLIUM. 

SILVER,  which  is  also  a  univalent  metal,  is  found 
in  nature  both  free  and  in  a  great  variety  of  com- 
pounds. The  native  metal,  pure  or  nearly  pure, 
sometimes  occurs  in  quite  large  masses ;  but  the 
more  important  ores  of  silver  are  compounds. 
Among  them  are  found  the  chloride,  bromide,  io- 
dide, sulphide,  and  telluride,  and  many  double 
compounds  containing  the  sulphide  united  with 
sulphides  of  arsenic  and  antimony.  In  some  cases 
the  silver  seems  to  be  merely  an  impurity,  as  in 
certain  ores  of  copper  and  lead,  from  which  the 
more  precious  metal  also  may  be  extracted. 

Silver  is  obtained  from  its  ores  by  a  great  va- 
riety of  processes,  concerning  which  a  treatise  on 
metallurgy  may  be  consulted.  Only  two  of  them 
can  be  considered  here.  First,  there  is  the  amal- 
gamation process,  which  is  essentially  as  follows: 
The  finely-powdered  ore  is  roasted  in  a  reverbera- 
tory  furnace  with  a  quantity  of  common  salt,  where- 
by the  silver  is  converted  into  chloride.  The  mass 
is  then  mixed  with  water  to  a  thin  paste,  and  shaken 
up  with  scrap-iron  in  revolving  casks  for  several 
hours.  The  iron  withdraws  the  chlorine  from  the 
silver,  thus : 


SILVER  AND    THALLIUM. 
2AgCl  +  Fe  =  FeCl2  +  Aga. 


197 


Mercury  is  next  added,  and  the  agitation  is  contin- 
ued until  an  amalgam  of  silver  and  mercury  is  ob- 
tained. From  this  the  mercury  is  distilled  off,  and 
the  silver,  often  containing  gold,  remains  behind. 


FlG.  42. — Pattinson's  Silver-Lead  Process. 

Secondly,  there  is  the  Pattinson  process,  by 
which  the  traces  of  silver  that  often  occur  in  lead- 
ores  may  be  separated  from  the  lead.  The  latter  is 
first  melted  and  allowed  partially  to  cool ;  crystals 
of  lead  separate  out,  and  are  removed  by  a  strainer, 
and  a  richer  alloy  is  left  behind.  This  is  remelted, 
and  the  process  of  partial  cooling  and  straining  is 


198  INORGANIC  CHEMISTRY. 

continued  until  an  alloy  containing  at  least  three 
hundred  ounces  of  silver  to  the  ton  is  obtained. 
This  alloy  is  then  cupelled — a  process  in  which  it  is 
melted  on  a  porous  bed  of  bone-ash  in  presence  of 
a  blast  of  air.  The  lead  is  oxidized,  the  fused  ox- 
ide is  absorbed  by  the  bone-ash,  and  at  last  a  button 
of  pure  silver  remains. 

Silver  is  a  brilliant  white  metal,  of  atomic  weight 
108,  and  specific  gravity  10.512.  Its  symbol  is  Ag, 
from  the  Latin  argentum.  It  melts  at  about  1040° 
C.,  and  at  very  high  temperatures  it  may  be  vapor- 
ized and  distilled.  Its  vapor  has  a  bright  blue  color. 
Melted  silver  absorbs  many  times  its  bulk  of  oxygen 
from  the  air,  and  gives  it  out  again  upon  cooling  ; 
often  so  suddenly  as  to  cause  an  explosive  spatter- 
ing (called  spitting]  of  the  semi-fluid  metal.  Silver 
is  the  best  known  conductor  of  heat  and  electricity, 
and  is  exceedingly  malleable  and  ductile.  In  the 
arts  it  is  usually  alloyed  with  a  little  copper,  which 
hardens  it.  The  American  coinage  standard  is  900 
fine — that  is,  1,000  parts  of  the  metal  used  for  coin- 
ing contain  900  parts  of  silver  to  100  of  copper. 
English  silver  coins  are  925  fine.  Jewelers'  silver 
is  generally  less  fine. 

The  compounds  of  silver  are,  with  a  few  excep- 
tions, formed  on  the  same  type  as  those  of  the  al- 
kali metals.  Thus,  we  have  an  oxide,  Ag2O  ;  a  sul- 
phate, Ag2SO4 ;  a  nitrate,  AgNO3 ;  and  a  chloride, 
AgCl.  In  general,  the  salts  of  silver  do  not  con- 
tain water  of  crystallization.  The  sulphide,  Ag2S, 
is  interesting  as  a  natural  ore,  and  on  account  of 
the  ease  with  which  it  is  produced  artificially.  The 
blackening  of  silver-ware  is  due  to  H2S  in  the  at- 
mosphere ;  and  the  blackening  of  spoons  by  eggs  is 


SILVER  AND    THALLIUM. 


199 


caused  by  the  sulphur  which  the  latter  contain. 
Pass  a  bubble  of  H2S  into  a  solution  of  silver  ni- 
trate, and  a  black  precipitate  of  silver  sulphide  will 
form. 

The  most  important  compounds  of  silver  are  the 
chloride  and  the  nitrate.  Some  of  their  relations 
to  each  other  and  to  the  metal  may  be  profitably 
studied  by  experiment. 

EXPERIMENT  82. — Cover  a  small  silver  coin, 
either  in  a  glass  beaker,  flask,  or  porcelain  dish, 
with  a  mixture  of  half-and-half  nitric  acid  and  wa- 
ter. Upon  heating,  the  coin  will  dissolve,  and  the 
solution  will  have  a  blue  color  due  to  the  copper 
which  is  present.  Add  a  solution  of  common  salt, 
Nad,  in  considerable  excess,  and  shake  vigorously. 
Silver  chloride,  which  is  insoluble,  will  be  precipi- 
tated, while  all  the  copper  will  remain  dissolved. 
Filter,  and  wash  the  precipitate  thoroughly  by 
pouring  water  over  it  until  the  liquid  runs  through 
colorless.  Transfer  the  silver  chloride,  still  moist, 
to  a  porcelain  dish,  add  some  clippings  of  zinc,  and 
cover  the  mixture  with  dilute  sulphuric  acid.  By 
the  action  of  the  latter  on  the  zinc,  hydrogen  will 
be  evolved,  which,  at  the  instant  of  its  liberation, 
in  the  nascent  state,  will  withdraw  chlorine  from  the 
silver  chloride,  forming  hydrochloric  acid,  and  set- 
ting the  metal  free.  When  all  the  zinc  has  been 
dissolved,  silver  will  remain  as  a  black,  spongy  mass, 
which  may  be  either  melted  into  a  globule  before 
the  blow-pipe,  or  dissolved  in  nitric  acid  to  form 
pure  AgNO3.  From  its  colorless  solution  the  latter 
compound  is  deposited  in  tabular,  transparent  crys- 
tals. This  experiment  shows,  on  a  small  scale,  the 
exact  method  by  which  the  officers  of  a  mint  or 


200  INORGANIC  CHEMISTRY. 

silver-refinery  prepare  pure  silver  from  crude  bull- 
ion. 

The  formation  of  silver  chloride  in  the  foregoing 
experiment  is  according  to  the  equation — 

AgNO3  +  NaCl  =  NaNO3  +  AgCl, 

and  well  illustrates  what  is  called  double  decomposi- 
tion. Silver  and  sodium  change  places,  as  also  do 
the  nitric-acid  radicle  and  chlorine ;  and  two  new 
salts  result  from  the  mutual  transfers.  We  have 
already  met  with  several  examples  of  this  sort 
of  chemical  change,  and  we  shall  meet  with  many 
more  as  we  go  on.  They  all  come  under  one  of 
two  laws,  which,  having  been  first  announced  by 
Berthollet,  are  known  as  Berthollefs  laws,  and  are  as 
follow  :  I .  Whenever  two  substances  in  solution  together 
are  capable  of  exchanging  atoms  so  as  to  form  a  compound 
insoluble  in  the  solvent  employed,  that  compound  will  be 
produced  and  deposited  as  a  precipitate.  2.  Whenever 
two  substances  in  mixture  are  capable  of  exchanging 
atoms  so  as  to  form  a  compound  which  is  gaseous  at  the 
temperature  of  the  experiment,  that  compound  will  be 
evolved  as  a  vapor  or  gas.  The  case  in  point  illus- 
trates the  first  law ;  the  second  may  be  exemplified 
by  heating  together  ammonium  chloride  and  hy- 
drogen sodium  carbonate.  Ammonium  carbonate, 
which  is  volatile,  will  be  set  free,  and  sodium  chlo- 
ride will  remain. 

NaHCO3  +  AmCl  =  NaCl  +  AmHCOs. 

In  the  actual  experiment  the  NH4,  HCO3  splits  up 
into  NH3  +  CO2  -t-  H2O.  This  particular  mixture 
has  been  proposed,  and  slightly  used,  for  a  baking- 
powder. 


SILVER  AND    THALLIUM.  2QI 

Silver  chloride,  as  obtained  in  Experiment  82,  is 
a  white,  curdy  precipitate  which  darkens  on  expos- 
ure to  light.  If  potassium  bromide  or  iodide  be 
used  in  place  of  common  salt,  silver  bromide  or 
iodide  will  be  thrown  down.  The  latter  is  yellow, 
the  bromide  is  yellowish  white.  All  these  com- 
pounds are  sensitive  to  light,  and  they  are  therefore 
of  great  importance  in  the  art  of  photography. 

We  have  already  seen,  in  studying  the  formation 
of  hydrochloric  acid,  that  light  may  bring  about 
chemical  union.  It  may  also  effect  chemical  de- 
composition ;  and  this  is  especially  the  case  with 
most  of  the  salts  of  silver.  All,  or  nearly  all  of 
them,  when  in  contact  with  organic  matter,  are 
blackened  by  light — most  where  the  light  is  strong- 
est, less  where  it  is  weaker.  This  fact  is  the  foun- 
dation principle  of  photography,*  which,  in  its 
commonest  form,  is  essentially  as  follows : 

A  glass  plate  is  first  coated  with  a  film  of  collo- 
dion, which  is  prepared  by  dissolving  gun-cotton  in 
a  mixture  of  alcohol  and  ether,  and  adding  to  it 
certain  bromides  or  iodides.  The  plate  is  next 
dipped  into  a  solution  whereof  silver  nitrate  is  the 
chief  ingredient,  and  either  the  bromide  or  iodide 
of  silver  is  precipitated  in  the  collodion-film.  Hav- 
ing been  thus  prepared  in  a  dark  room,  the  plate  is 
transferred  to  the  photographic  camera,  and  the 
image  of  the  scene  or  object  to  be  photographed 
is  allowed  to  fall  upon  it.  Where  the  object  is 
light,  the  plate  is  strongly  affected  ;  where  it  is 

*  Captain  Abney's  "  Treatise  on  Photography  "  is  one  of  the  best 
of  the  smaller  works  on  this  subject ;  Vogel's  "  Chemistry  of  Light 
and  Photography"  ("International  Scientific  Series,"  vol.  xiv)  is  also 
very  good. 


202  INORGANIC  CHEMISTRY. 

dark,  the  action  is  slighter;  so  that  the  picture 
which  is  produced  has  all  its  lights  and  shadows 
reversed,  and  is  called  a  "  negative."  When  first 
taken  from  the  camera,  the  plate  shows  no  signs  of 
alteration  ;  but  the  image  is  brought  out  by  pour- 
ing over  the  plate  a  chemical  solution  known  as 
the  developer.  For  this  purpose  various  substances 
are  used,  ferrous  sulphate  being  the  commonest.* 
Finally,  the  plate  is  washed  with  a  solution  of  sodium 
thiosulphate,  which  dissolves  out  the  silver  salts 
which  have  been  unattacked,  and  the  picture  is  thus 
rendered  permanent.  In  "  printing  "  from  this  nega- 
tive, a  sheet  of  paper  is  rendered  sensitive  by  silver 
nitrate,  and  exposed  underneath  the  plate  to  the 
action  of  strong  sunlight.  Where  the  negative  is 
dark  the  paper  remains  light,  and  vice  versa ;  so 
that  an  image  which  is  correct  as  to  lights  and 
shadows  is  produced.  This,  too,  is  "  fixed  "  by  so- 
dium thiosulphate,  and,  after  some  little  details  of 
finishing,  the  photograph  is  done. 

EXPERIMENT  83. — Soak  a  sheet  of  white  paper 
in  a  solution  of  silver  nitrate.  Place  over  it  a  piece 
of  lace  or  a  fern-leaf,  cover  it  by  a  sheet  of  glass, 
and  expose  it  to  the  sunshine  until  all  the  uncov- 
ered portions  are  darkened.  Wash  it  in  a  dark 
room  or  closet,  first  with  a  solution  of  sodium  thio- 
sulphate, and  afterward  with  pure  water,  continu- 
ing the  latter  until  the  rinsings  no  longer  have  a 
sweetish  taste.  A  perfect  copy  of  the  lace  pattern 
or  leaf  will  remain  as  a  photographic  print  on  the 
paper. 

Silver  nitrate,  which  is  always  prepared  by  dis- 

*  The  theory  of  the  action  of  the  developer  is  somewhat  obscure, 
and  would  be  out  of  place  in  this  treatise. 


SILVER  AND    THALLIUM.  203 

solving  silver  in  nitric  acid,  occurs  in  commerce 
in  two  forms :  First,  we  find  it  in  large,  trans- 
parent, tabular  crystals,  in  which  form  it  is  used 
for  various  laboratory  purposes,  by  the  photogra- 
phers, and  in  the  art  of  electroplating ;  second, 
the  fused  salt  is  cast  in  small,  round  sticks,  which 
are  used  by  physicians  under  the  name  of  "  lunar 
caustic."  It  is  applied  to  the  cautery  of  inflamed 
surfaces. 

When  a  little  potassium  cyanide,  KCN,  is  added 
to  a  solution  of  silver  nitrate,  a  precipitate  of  silver 
cyanide,  AgCN,  closely  resembling  the  chloride,  is 
formed.  Upon  the  addition  of  more  KCN,  the 
precipitate  redissolves,  and  a  solution  is  produced 
which  is  much  used  in  silver-plating.*  In  such  a 
solution,  the  preparation  of  which  is  subject  to 
many  variations,  the  object  to  be  plated  is  im- 
mersed, together  with  a  bar,  rod,  or  plate  of  pure 
silver.  The  latter  is  connected  by  a  wire  with  the 
negative  element  of  a  battery,  while  the  object  to 
be  plated  is  connected  with  the  other  pole.  When 
the  current  passes,  electrolysis  takes  place,  and  sil- 
ver is  deposited  upon  the  object  in  a  thin,  coherent 
film.  At  the  same  time  silver  is  dissolved  off  from 
the  plate  at  the  opposite  pole.  The  process  con- 
tinues until  the  plating  has  acquired  whatever 
thickness  may  be  demanded ;  afterward  the  plated 
article  is  washed  and  polished.  The  same  general 
method,  but  with  different  solutions,  is  employed 
in  plating  with  gold,  copper,  platinum,  or  nickel. 

THALLIUM,  atomic  weight  204,  is  one  of  the  very 
rare  metals.  It  was  discovered  in  1861  by  Crookes, 

*  For  full  details  as  to  solutions  and  processes,  see  Gore's  "  Elec- 
tro-Metallurgy." 


204  INORGANIC  CHEMISTRY. 

with  the  aid  of  the  spectroscope,  and  in  its  general 
properties  it  strongly  resembles  lead.  Its  com- 
pounds give  a  brilliant  green  color  to  flame,  and 
are  mostly  poisonous.  It  forms  two  sets  of  salts — 
the  thallious  and  thallic  compounds ;  behaving  like 
a  univalent  element  in  the  first,  and  being  trivalent 
in  the  second.  It  occurs  as  an  impurity  in  iron 
pyrites  and  in  native  sulphur,  and  is  usually  ob- 
tained from  the  flue-dust  of  sulphuric-acid  works. 


CHAPTER   XXII. 

CALCIUM,    STRONTIUM,   AND   BARIUM. 

THE  bivalent  metals  are  quite  numerous,  and 
form  several  well-defined  sub-groups.  In  one  of 
these  we  find  the  three  closely  allied  metals  whose 
names  head  this  chapter. 


Atomic  weight. 

Specific  gravity. 

Calcium  Ca 

4.O 

1.58 

Strontium,  Sr  

87.5 

3« 

2.58 

Barium   Ba 

1  17 

-3  7C 

In  general,  strontium  and  its  compounds  have 
properties  nearly  midway  between  those  of  the 
other  two  metals.  For  instance,  strontium  sulphate 
is  less  soluble  in  water  than  calcium  sulphate,  and 
more  so  than  barium  sulphate ;  and  in  specific 
gravity  it  also  lies  between  the  two.  In  short,  if 
we  know  the  properties  of  two  corresponding  salts 
of  barium  and  calcium,  we  can  make  a  close  guess 
as  to  what  the  properties  of  the  similar  strontium 
salt  will  be.  The  metals  themselves  are  unimpor- 
tant, and  difficult  to  obtain.  Calcium  is  yellow, 
strontium  yellowish,  barium  white.  All  three  are 
fusible  only  above  a  red  heat,  all  oxidize  easily  in 
the  air,  all  are  malleable  and  ductile. 


206 


INORGANIC  CHEMISTRY. 


CALCIUM  is  one  of  the  most  abundant  of  ele- 
ments. As  carbonate  we  find  it  in  nature  in  the 
form  of  limestone,  marble,  chalk,  coral,  marl,  etc. 
It  enters  into  the  composition  of  many  silicates; 
the  sulphate,  fluoride,  and  phosphate  are  abundant 
minerals ;  and  the  phosphate  is  also  an  important 
ingredient  of  plants  and  of  bones. 

Calcium  oxide,  CaO,  is  commonly  known  as 
quicklime.  It  is  always  prepared  by  heating  the 
carbonate,  which  is  decomposed  in  accordance  with 
the  following  reaction : 

CaCO3  =  CaO  +  COa. 

On  a  large  scale,  limestone  is  burned  in  a  lime-kiln 
(Fig.  43),  and  the  lime  remains  behind.  It  is  a 
white,  infusible  solid,  which 
unites  violently  with  water, 
evolving  great  heat,  and  form- 
ing  the  hydroxide,  CaH2O2. 
The  latter  formula  may  also  be 
written  Ca(OH)2,  to  illustrate 
the  bivalency  of  the  metal. 

Calcium  hydroxide,  or 
slaked  lime,  is  a  very  useful 
compound.  The  heat  attend- 
ing its  formation  may  be  ob- 
served by  sprinkling  a  lit- 
tle cold  water  over  a  lump 
of  lime  and  noting  that  steam 
is  evolved.  Fires  are  often 

caused  by  the  accidental  contact  of  water  with 
lime  which  has  been  stored  in  leaky  buildings. 
Under  such  circumstances,  in  a  closed  space,  the 
heat  may  be  sufficient  to  kindle  wood. 


FIG.  43. — Lime-Kiln. 


CALCIUM,   STRONTIUM,  AND  BARIUM.     207 

Just  as  sodium  hydroxide  is  called  caustic  soda, 
so  calcium  hydroxide  is  often  called  caustic  lime. 
It  has  a  strong-  alkaline  reaction,  neutralizes  acids, 
and  attacks  organic  matter  vigorously.  It  is  often 
used  as  a  fertilizer,  inasmuch  as  it  helps  to  rot  or- 
ganic substances  in  the  soil ;  and  in  tanneries  it  is 
applied  to  hides  to  aid  in  the  removal  of  hair.  As 
milk  of  lime — that  is,  suspended  in  water — it  serves 
as  whitewash ;  and  it  is  also  used  in  purifying  coal- 
gas,  in  making  bleaching-powder  and  the  caustic 
alkalies,  and  for  a  great  variety  of  other  chemical 
purposes.  But  the  larger  uses  of  slaked  lime  are 
in  the  preparation  of  mortars  and  cements.  Mortar 
is  made  by  mixing  lime  with  water  and  sand ;  for 
interior  plastering  hair  is  added,  to  bind  the  mass 
together.  When  first  mixed,  mortar  is  soft  and 
pasty ;  on  drying  it  hardens,  absorbs  carbon  di- 
oxide from  the  air,  and  forms  a  substance  which  in 
time  becomes  almost  as  compact  as  stone.  In  very 
old  brick-work,  the  mortar  is  often  harder  and 
stronger  than  the  bricks  themselves.  Hydraulic 
lime,  which  forms  a  cement  capable  of  hardening 
under  water,  is  made  by  burning  a  limestone  mixed 
with  clay. 

The  extensive  occurrence  of  calcium  carbonate 
in  nature  has  already  been  noticed.  In  its  purest 
state  this  substance  forms  transparent  crystals, 
which  vary  remarkably  in  character.  One  variety 
is  known  as  Iceland-spar  (Fig.  44),  and  is  doubly 
refracting — that  is,  a  line  or  object  seen  through  it 
appears  to  be  doubled.  Iceland-spar  is  much  used 
in  instruments  for  studying  polarized  light.  In 
pure  water  calcium  carbonate  is  very  slightly  solu- 
ble ;  more  so  in  water  containing  carbonic  acid. 


208  INORGANIC  CHEMISTRY. 

EXPERIMENT  84. — Into  a  test-tube  filled  with 
lime-water  pass  a  bubble  of  carbon  dioxide.     Cal- 


FlG.  44. — Double  Refraction. 

cium  carbonate  will  be  thrown  down  as  a  white 
precipitate,  but,  if  a  stream  of  the  gas  be  passed 
in  for  a  longer  time,  it  will  again  dissolve.  Upon 
boiling  the  clear  solution  the  excess  of  CO2  will  be 
driven  off,  and  CaCO3  will  be  reprecipitated. 

It  is  by  this  solvent  action  of  water  charged 
with  carbon  dioxide  that  great  limestone  caverns, 
like  the  Mammoth  Cave  of  Kentucky,  are  formed. 
From  the  roof  of  such  a  cave,  especially  during  its 
period  of  formation,  water  continually  drips.  Each 
drop,  in  falling,  leaves  behind  a  particle  of  its  dis- 
solved limestone,  and  deposits  another  particle 
upon  the  floor  beneath.  Thus,  in  the  course  of 
ages,  a  stalactite  grows  slowly  downward,  like  a 
stone  icicle,  from  above ;  while  from  below  a  sta- 
lagmite rises  gradually  to  meet  it.  If  the  process 
continues  long  enough,  a  column  of  semi-transpar- 
ent calcium  carbonate  is  the  result. 

Calcium  sulphate,  crystallized  with  two  mole- 
cules of  water,  occurs  abundantly  in  nature  as  gyp- 
sum, CaSO4,  2H2O.  In  white,  translucent  masses,  it 
is  used  as  an  ornamental  stone,  and  is  known  as  ala- 


CALCIUM,   STRONTIUM,  AND  BARIUM.    209 

baster ;  in  regular,  transparent  crystals,  it  is  called 
selenite.  Gypsum  is  somewhat  important  as  a  fer- 
tilizer ;  and,  when  deprived  of  its  water  by  calcina- 
tion, it  forms  plaster  of  Paris.  The  latter  substance, 
when  mixed  to  a  thin  paste  with  water,  reabsorbs 
the  two  molecules  which  were  lost  on  calcination, 
and  "  sets  "  to  a  compact,  solid  mass.  In  solidify- 
ing it  also  expands ;  and  to  this  fact  is  partly  due 
its  value  in  making  casts.  When  poured  into  a 
mold,  it  forces  its  way  into  every  crack  and  crev- 
ice, and  thus  a  perfect  copy  is  insured. 

Like  calcium  carbonate,  calcium  sulphate  is 
slightly  soluble  in  water ;  and  in  natural  waters 
both  compounds  often  occur.  Such  waters  are 
popularly  known  as  "  hard  "  waters,  and  are  objec- 
tionable for  washing  purposes  or  for  use  in  the 
steam-boiler.  In  the  latter  case,  the  lime-salts  are 
liable  to  be  deposited  on  the  sides  of  the  boiler  as 
a  hard,  coherent  coating,  called  boiler -crust  or 
boiler-scale,  which,  being  a  non-conductor  of  heat, 
causes  great  waste  of  fuel.  In  the  laundry,  lime- 
salts  react  upon  the  soap  which  is  used,  and  insol- 
uble lime-soaps  are  precipitated ;  so  that  no  good 
soapy  effect  can  be  produced  until  all  the  calcium 
compounds  have  been  eliminated. 

Calcium  fluoride,  CaF2,  has  already  been  referred 
to  in  connection  with  fluorine.  It  is  a  mineral  which 
crystallizes  in  cubes,  often  brilliantly  colored,  and  is 
useful  in  the  preparation  of  hydrofluoric  acid.  The 
nitrate,  Ca(NO3)2,  is  found  in  the  soil  of  some  caves, 
and  when  abundant  may  be  profitably  treated  with 
potassium  carbonate,  and  made  a  source  of  salt- 
peter. The  phosphate,  Ca3(PO4)2>  is  found  in  bones, 
and  also,  combined  with  a  little  fluoride  or  chloride, 


210  INORGANIC  CHEMISTRY. 

in  great  beds  as  a  mineral.  It  is  valuable  as  a  fer- 
tilizer ;  and,  when  treated  with  sulphuric  acid,  it 
yields  the  so-called  "  superphosphate,"  CaHPO4, 
which  is  much  used  in  agriculture. 

Calcium  hypochlorite,  chloride  of  lime,  or  bleach- 
ing-powder,  has  already  been  described.  Calcium 
chloride,  CaCl2,  which  is  prepared  by  dissolving 
chalk  or  marble  in  hydrochloric  acid  and  evaporat- 
ing to  dryness,  is  a  white,  soluble  compound  much 
used  in  the  laboratory.  It  absorbs  moisture  with 
great  avidity ;  enough  in  damp  air  to  actually  dis- 
solve itself ;  and  is,  therefore,  of  great  value  in 
drying-  gases.  It  is  also  employed  in  making 
some  kinds  of  artificial  stone.  The  crystallized  salt, 
CaCl2,  6H2O,  mixed  with  pounded  ice  or  snow, 
gives  a  powerful  freezing  mixture ;  and  with  it  a 
temperature  as  low  as  — 48.5°  has  been  obtained. 

STRONTIUM,  as  compared  with  calcium,  is  rare 
and  comparatively  unimportant.  Its  sulphate  and 
carbonate  occur  as  beautifully  crystallized  minerals. 
Its  compounds  give  a  rich  red  color  to  flame,  and 
on  this  account  its  nitrate,  Sr(NO3Xj,  and  its  chlo- 
rate, Sr(ClO3)2,  are  used  in  the  red-fire  mixtures 
of  the  pyrotechnist.  Most  of  these  mixtures  con- 
tain sulphur,  and  therefore  smell  badly  when  burn- 
ing ;  but  the  following  experiment  may  be  tried  in 
a  room : 

EXPERIMENT  85. — Take  two  parts  of  potassium 
chlorate,  two  of  strontium  nitrate,  and  one  of  shel- 
lac. Powder  them  separately,  and  finely,  and  mix  on 
paper  with  as  little  friction  as  possible.  Kindle  the 
mixture  in  any  convenient  vessel,  and  it  will  give 
the  brilliant  strontium  -  flame.  The  ingredients 
should  be  weighed  out,  and  all  should  be  scrupu- 


CALCIUM,   STRONTIUM,  AND  BARIUM.     2ll 

lously  dry.*  If  barium  nitrate  be  used  in  place  of 
the  strontium  salt,  a  green-fire  mixture  will  be  made. 

BARIUM  is  much  more  plentiful  than  strontium  ; 
but,  like  the  latter  metal,  it  occurs  mainly  as  sul- 
phate and  carbonate.  It  is  also  found  in  a  few 
rather  uncommon  silicates.  Several  of  its  com- 
pounds have  practical  interest.  The  chloride,  BaCl2, 
2H2O,  and  the  carbonate,  BaCO3,  are  useful  reagents 
in  qualitative  analysis ;  and,  as  above  indicated,  its 
nitrate  is  employed  by  the  pyrotechnist  in  making 
green  fire.  There  are  two  oxides  of  barium,  BaO 
and  BaO2,  and  these  are  easily  transformable,  the 
one  into  the  other.  Upon  this  fact  a  "  regenera- 
tive "  process  for  making  oxygen  has  been  based. 
The  monoxide,  BaO,  heated  in  a  stream  of  air,  is 
converted  by  direct  oxidation  into  BaO2.  The  lat- 
ter, heated  more  strongly,  gives  up  its  extra  atom 
of  oxygen,  leaving  BaO  ready  to  be  recharged  in 
another  air-current.  The  operation  may  be  re- 
peated indefinitely.  The  BaO  serves  as  a  carrier 
by  which  oxygen  may  be  withdrawn  from  the  at- 
mosphere and  transferred  to  a  gas-holder. 

Barium  sulphate,  BaSO4,  is  noted  for  its  insolu- 
bility. Add  sulphuric  acid  or  a  solution  of  any 
other  sulphate  to  a  solution  containing  barium,  and 
BaSO4  will  be  thrown  down  as  a  heavy  white 
powder.  Hence  sulphuric  acid  serves  as  a  test  for 
barium,  and  vice  versa.  The  precipitated  compound 
is  somewhat  used  as  a  white  paint,  under  the  name 
of  blanc  fixe ;  and  the  natural  sulphate,  which  is 
commonly  called  barytes  or  heavy  spar,  is  ground 

*  A  good  list  of  recipes  for  different  colored  fires  is  given  in  Sadt- 
ler's  "Chemical  Experimentation,"  p.  202.  The  book  is  a  useful  one 
for  either  pupils  or  teachers. 


212  INORGANIC  CHEMISTRY. 

up  as  an  adulterant  for  white-lead.  By  heating 
the  sulphate  with  charcoal,  the  sulphide,  BaS,  is 
produced.  This  substance,  exposed  to  a  strong 
light,  is  afterward  luminous  in  the  dark.  The  sul- 
phides of  calcium  and  strontium  have  similar  prop- 
erties, and  from  either  of  the  three  a  luminous  paint 
may  be  made. 


CHAPTER  XXIII. 

SPECTRUM  ANALYSIS.* 

WHEN  a  beam  of  sunlight  passes  through  a  glass 
prism,  and  falls  upon  a  white  screen,  colors  are  pro- 
duced, and  the  unaided  eye  readily  distinguishes  at 
least  seven  tints.  These  are  red,  orange,  yellow, 
green,  blue,  indigo,  and  violet,  and  are  popularly 
known  as  the  seven  primary  colors.  If  the  prism 
is  placed  in  a  dark  chamber,  and  the  light  is  ad- 
mitted only  through  a  narrow  slit,  the  colors  ar- 
range themselves  in  a  long  band,  side  by  side,  with 
the  red  at  one  end  and  the  violet  at  the  other,  and 
the  remaining  tints  occupying  their  proper  order 
between.  In  the  sunbeam  these  colors  are  all  mixed 
together,  and  the  effect  of  the  prism  merely  is  to 
separate  them,  by  virtue  of  their  differences  in  re- 
frangibility. 

Suppose  now  that,  instead  of  sunlight,  some 
colored  flame  be  studied  with  the  prism,  what  sort 
of  a  color-band  or  spectrum  shall  we  obtain?  In 
every  case  we  shall  have,  not  a  continuous  band  of 
colors,  but  one  or  more  bright-colored  lines,  sepa- 

*  In  a  treatise  on  chemistry  this  subject  can  be  considered  only  on 
its  chemical  side.  The  physical  theory  of  the  spectroscope,  the  nature 
of  luminous  waves,  etc.,  can  be  properly  studied  only  as  a  branch  of 
physics. 


214 


INORGANIC  CHEMISTRY. 


rated  from  each  other  by  dark  spaces ;  and  these 
lines  will  be  absolutely  characteristic  of  the  sub- 
stance to  which  the  tint  of  the  flame  is  due.  A 
compound  of  sodium  will  give  one  bright-yellow 
line  ;  potassium,  a  red  and  a  violet ;  thallium,  a  green 
line  ;  strontium,  a  cluster  in  the  red  and  orange, 
and  one  brilliant  line  in  the  blue  ;  barium,  a  number 
of  lines  near  together,  and  mainly  in  the  green 
and  y-ellow  portions  of  the  spectrum ;  lithium,  a 
very  rich  line  in  the  red,  etc.  There  are  also  some 
fainter  lines  which  need  not  be  mentioned  here  ; 
and  occasionally  lines,  which  seem  at  first  to  be 
single,  prove  when  magnified  to  consist  of  several 
closely  huddled  together.  The  yellow  line  of  so- 
dium, for  instance,  is  really  double.  In  no  case  does 
any  element  give  a  line  belonging  to  any  other ;  so 
that  if  we  insert  any  substance  in  a  flame  and  exam- 
ine its  spectrum,  we  can  determine  at  once  which  of 
the  above-named  elements  it  contains.  This  meth- 
od of  examination  is  called  spectrum  analysis ;  and  it 
is  well  illustrated  by  the  colored  chart  of  spectra 
which  is  the  frontispiece  to  this  volume. 

In  order  that  spectra  may  be  conveniently  stud- 
ied, an  instrument  called  the  spectroscope  has  been 
devised.  This,  like  most  other  great  inventions, 
grew  up  step  by  step,  one  discoverer  after  another 
adding  some  point  or  detail ;  but  the  honor  of  com- 
pleting and  perfecting  the  instrument  is  chiefly  due 
to  Professor  Bunsen,  of  Heidelberg  in  Germany. 
In  its  simplest  form  it  is  constructed  as  follows 

(Fig-  45) : 

A  prism  and  two  small  telescopes  are  mounted 

upon  a  circular  metallic  plate  and  stand,  as  shown 
in  the  illustration.  One  telescope,  which  serves  for 


SPECTR  UM  ANAL  YSIS.  2 1-5 

receiving  the  light  to  be  examined,  is  closed  at  its 
outer  end  by  two  metallic  knife-edges,  which  may 


FIG.  45. — One-Prism  Spectroscope. 

be  moved  nearer  together  or  farther  apart,  and 
which  furnish  the  narrow  slit  as  previously  indi- 
cated. The  second  telescope  is  used  for  observ- 
ing the  spectrum.  The  light  enters  the  slit,  passes 
through  the  collecting-telescope,  and  falls  upon  the 
prism.  There  it  is  refracted  and  dispersed,  and  is 
seen  through  the  observing  eye-piece  as  the  long 
band  which  was  described  in  a  previous  paragraph. 
In  nice  instruments  the  observing  eye-piece  con- 
tains a  pair  of  cross-hairs,  and  is  movable,  with  its 
telescope,  from  side  to  side ;  and  the  metallic  plate 
which  supports  it  is  provided  with  a  graduated  cir- 
cle. Then,  by  moving  the  telescope  so  as  to  bring 
each  spectral  line  exactly  across  the  intersection  of 
the  cross-hairs,  its  position  relatively  to  other  lines 
may  be  accurately  measured.  With  these  additions 
the  spectroscope  becomes  also  a  spectrometer,  and  is 
a  most  convenient  instrument  for  many  optical  in- 


2i6  INORGANIC  CHEMISTRY. 

vestigations.  Instead  of  one  prism,  a  spectroscope 
may  contain  several  prisms,  and  so  be  greatly  in- 
creased in  power  (Fig.  46). 

Another  convenient  form  of  instrument  is  the 


FIG.  46. — Diagram  of  a  Train  of  Prisms,  with  Telescopes. 

direct-vision  spectroscope.  In  the  ordinary  spectro- 
scope the  light  is  so  refracted  that  the  two  tele- 
scopes form  an  angle  with  each  other;  and  it  is 
often  a  tedious  matter  to  adjust  them  relatively  to 
the  prism  in  the  proper  position.  In  the  direct- 
vision  spectroscope  the  prisms,  which  may  number 
three,  five,  seven,  or  nine,  are  arranged  as  shown 
in  Fig.  47,  and  no  adjustment  is  necessary.  Such 
spectroscopes  are  now  made  very  cheaply,  and 
small  enough  to  be  carried  in  the  vest-pocket.  For 
many  purposes  they  are  very  handy  and  useful. 
In  the  laboratory  the  spectroscope  is  mainly 


SPECTRUM  ANALYSIS. 


217 


used  for  detecting  Li,  Na,  K,  Cs,  Rb,  Tl,  Ca,  Sr, 
Ba,  B,  or  Cu ;  all  of  which  substances  impart  defi- 
nite colors  to  a  gas  or  alcohol  flame.  The  usual  plan 
is  to  put  a  little  of  the  substance  under  examination 
upon  a  piece  of  clean  platinum  wire,  and  insert  it 
in  the  flame  of  a  Bunsen  gas-burner.  Then,  al- 
most at  a  glance,  whatever  spectra  may  be  present 
can  be  recognized.  Some  of  the  tests  are  inconceiv- 
ably delicate — for  example,  rgiFTjimnnr  °f  a  grain  of 
sodium,  or  OTirinnr  of  a  grain  of  lithium,  will  reveal 


FIG.  47. — Section  of  a  Direct -vision  Spectroscope. 

its  presence  immediately.  Several  of  the  rarer 
metals  have  been  discovered  by  means  of  the  spec- 
troscope— namely,  caesium,  rubidium,  thallium,  in- 
dium, and  gallium.  Caesium  and  rubidium  were 
discovered  by  Bunsen  himself,  shortly  after  the  in- 
vention of  the  instrument.  He  applied  his  spec- 
troscope to  the  examination  of  a  mineral  water,  and 
observed  certain  lines  which  belonged  to  no  known 
element.  He  at  once  inferred  that  some  new  ele- 
ment must  be  present ;  and,  carefully  searching, 
obtained  the  chlorides  of  the  two  metals.  At  the 
high  temperature  of  the  electric  arc  all  the  ele- 
ments give  characteristic  spectra,  and  most  of  them 
have  been  carefully  mapped  and  examined. 

Another  laboratory  use  of  the  spectroscope  is  in 
the  identification  of  dissolved  coloring-matters.     If 


2iS  INORGANIC  CHEMISTRY. 

a  beam  of  sunlight  be  passed  through  a  solution  of 
blood,  cochineal,  logwood,  etc.,  a  red  light  will  be 
transmitted  ;  other  solutions  transmit  green,  yellow, 
or  blue  tints  mainly.  If  the  transmitted  light  be 
examined  with  the  spectroscope,  certain  parts  of 
the  complete  spectrum  will  be  found  to  be  blotted 
out,  and  what  is  called  an  absorption  spectrum  will  be 
seen.  Such  a  spectrum  is  in  most  cases  character- 
istic of  the  coloring-matter  which  produces  it,  and 
at  once  reveals  the  presence  of  the  latter.  The  ar- 
tificial color  of  an  adulterated  red  wine  may  thus 
(with  some  limitations)  be  detected. 

Whenever  we  have  a  spectrum  consisting  of 
bright  lines  with  dark  spaces  between,  it  is  pro- 
duced by  heated  matter  in  the  condition  of  a  gas. 
All  the  elements  above  mentioned,  which  color  the 
Bunsen  flame,  do  so  in  the  form  of  compounds 
which  are  gaseous  at  its  temperature.  The  other 
elements,  as  was  already  stated,  require  much  more 
elevated  temperatures  for  the  production  of  bright- 
line  spectra. 

If  we  study  the  light  emitted  by  highly  incan- 
descent solids,  such  as  the  carbon  of  an  electric  arc 
or  the  lime  cylinder  in  the  oxyhydrogen-flame,  we 
shall  find  that  it  gives  a  spectrum  without  lines,  and 
brilliantly  continuous  from  the  red  end  to  the  vio- 
let. In  the  spectrum  of  sunlight,  however,  we  have 
something  different  still — namely,  a  continuous  spec- 
trum intersected  by  a  vast  number  of  fine  black  lines, 
each  of  which  occupies  a  fixed  and  definite  position.* 
These  lines  were  first  described  by  Wollaston  ;  and 
later  they  were  carefully  mapped  by  Fraunhofer ; 

*  Dark  lines  running  lengthwise  of  the  spectrum  often  confuse  the 
beginner.     They  are  due  to  dust-specks  on  the  slit  of  the  spectroscope. 


SPECTRUM  ANALYSIS. 


2I9 


they  are  now  known  as  Fraimhofer's  lines.  Each 
of  them  corresponds  in  position  exactly  with  one  of 
the  bright  lines  obtainable  from  a  chemical  element ; 
for  example,  Fraunhofer's  line  "  D,"  in  the  yellow, 
coincides  precisely  with  the  sodium-line,  and,  like 
the  latter,  is  really  double.  What  does  this  mean  ? 
The  explanation,  discovered  by  the  joint  labors  of 
Professors  Bunsen  and  Kirchhoff,  is  simple,  and  is  an 
application  of  the  physical  law  that  substances  when 
cold  absorb  the  same  rays  which  they  give  out  when  hot. 
Let  us  consider  a  special  case  arising  under  this 
law.  Suppose  we  arrange  a  spectroscope  as  in  Fig. 
48,  and  place  in  front  of  the  slit  a  strong  light  capa- 


FIG.  48. — Reversal  of  Sodium-line. 

ble  of  giving  a  continuous  spectrum.  Now  between 
this  light  and  the  slit  interpose  a  layer  of  sodium  va- 
por, produced  by  heating  a  little  metallic  sodium 
in  an  iron  spoon.  The  part  of  the  spectrum  corre- 
sponding to  the  sodium-line  will  be  absorbed,  and 
a  dark  line  will  be  seen  in  its  place.  That  is,  sodium 
vapor  absorbs  the  yellow  ray  which  more  intensely 
heated  sodium  vapor  emits.  This  is  commonly 


220  INORGANIC  CHEMISTRY. 

known  as  the  reversal  of  the  sodium-line ;  and  the 
lines  of  other  elements  may  be  similarly  reversed. 
The  spectrum  of  sunlight  is  merely  a  continuous 
spectrum,  with  the  reversed  lines  of  over  twenty  of 
the  chemical  elements  distributed  in  their  proper 
places  through  it.  The  conclusion  is,  that  the  sun 
contains  these  elements  in  the  gaseous  condition ; 
and  through  such  a  gaseous  envelope  the  light  of  the 
solid  or  liquid  interior  is  transmitted.  In  short,  by 
means  of  the  spectroscope  we  can  analyze  the  heav- 
enly bodies,  and  tell  of  what  substances  they  are  com- 
posed. 

In  the  solar  spectrum,  so  far,  lines  belonging  to 
the  following  elements  have  been  identified :  iron, 
titanium,  calcium,  manganese,  nickel,  cobalt,  chro- 
mium, barium,  sodium,  magnesium,  copper,  hydro- 
gen, palladium,  vanadium,  molybdenum,  strontium, 
lead,  uranium,  aluminum,  cerium,  cadmium,  and 
oxygen.  The  presence  of  still  other  elements  in 
the  sun  has  been  less  clearly  made  out,  but  is  highly 
probable ;  and  in  several  of  the  fixed  stars,  which 
resemble  the  sun  in  character,  several  substances 
not  discoverable  in  the  sun  have  been  distinctly 
recognized.  The  bright  star  Aldebaran,  for  in- 
stance, contains  hydrogen,  sodium,  magnesium,  cal- 
cium, iron,  antimony,  mercury,  bismuth,  and  tellurium. 

At  various  points  in  the  heavens  are  seen  faint 
clouds  of  light,  called  nebulas.  Some  of  them  are 
star-clusters,  so  distant  that  only  a  powerful  tel- 
escope can  recognize  their  true  character ;  and 
such  nebulae  give  regular  star -spectra.  Others, 
however,  when  examined  with  the  spectroscope, 
prove  to  be  immense  clouds  of  incandescent  gas, 
and  give  a  bright-line  spectrum  indicating  hydro- 


SPECTRUM  ANALYSIS.  22l 

gen.  This  fact  has  a  curious  theoretical  impor- 
tance. It  is  commonly  held  by  scientific  men  that 
the  solar  system  was  once  a  vast  nebula,  which 
gradually  cooled  and  condensed  into  its  present 
condition  ;  and  a  great  deal  of  evidence,  physical 
and  mathematical,  can  be  cited  in  favor  of  this  neb- 
ular hypothesis.  In  the  heavens  we  see  all  stages  of 
development — from  the  nebula  itself,  down  to  the 
hotter  stars,  the  sun,  and  the  solid  planets ;  and  ac- 
companying this  progression,  we  find  a  steady  in- 
crease in  chemical  complexity.  The  nebulae  con- 
tain but  one  or  two  elements ;  the  whitest  and 
hottest  stars  a  few  more ;  stars  like  our  sun  a  larger 
number  still ;  and  at  last  we  find  the  earth  with  its 
multitude  of  compound  bodies.  From  these  facts 
we  arrive  at  once  at  a  startling  conclusion,  which, 
though  not  yet  absolutely  proved,  is  sustained  by 
many  lines  of  evidence,  and  is  yearly  becoming 
more  and  more  probable ;  namely,  that  the  evolu- 
tion of  planets  from  nebulae  has  been  accompanied 
by  an  evolution  of  the  chemical  elements  from  still 
simpler  forms  of  matter ;  and  that  matter  itself,  like 
force,  instead  of  being  many  different  things,  is 
really  at  bottom,  in  the  final  analysis,  one.* 

*  The  student  who  cares  to  pursue  the  subject  of  celestial  spec- 
troscopy  further  may  profitably  begin  with  two  volumes  in  the  "  Inter- 
national Scientific  Series  "  :  Young's  work  on  "  The  Sun,"  and  Lock- 
yer's  "  Studies  in  Spectrum  Analysis." 


CHAPTER    XXIV. 

GLUCINUM,    MAGNESIUM,   ZINC,   CADMIUM,  AND   MER- 
CURY. 

ALTHOUGH  the  metals  described  in  this  chapter 
are  all  bivalent,  they  do  not  form  as  definite  a  nat- 
ural group  as  some  that  we  have  been  considering. 
Magnesium  and  zinc,  indeed,  are  very  closely  re- 
lated ;  so  are  zinc  and  cadmium ;  and,  though  less 
strikingly,  so  also  are  cadmium  and  mercury.  But 
between  magnesium  and  mercury,  except  as  re- 
gards valency,  the  resemblances  are  quite  remote. 

GLUCINUM,  often  called  beryllium,  is  a  rare  metal 
of  specific  gravity  2.1,  and  an  atomic  weight  of  9. 
It  is  found  in  a  few  minerals,  among  which  the 
beryl  and  the  chrysoberyl  are  the  only  important 
species.  The  beryl  is  a  silicate  of  glucinum  and 
aluminum,  and  varies  in  color  from  white  to  yel- 
low, and  bluish  to  deep  green.  It  is  valuable  as  a 
gem ;  the  bluish  variety  being  known  as  aqua- 
marine, and  the  green  variety  as  the  emerald.  The 
salts  of  glucinum  are  all  formed  on  a  simple  biva- 
lent type,  and  in  their  outward  properties  have 
some  resemblance  to  the  compounds  of  trivalent 
aluminum.  The  oxide,  G1O,  the  chloride,  G1C12, 
and  the  sulphate,  G1SO4,  are  good  examples  of 
their  chemical  structure. 


GLUCINUM,  MAGNESIUM,   ZINC,   ETC.       223 

MAGNESIUM,  atomic  weight  24,  is  one  of  the 
more  abundant  elements,  and  forms  an  important 
part  of  the  earth's  crust.  It  occurs  in  many  sili- 
cates, such-  as  talc  and  serpentine ;  and  in  dolo- 
mite, a  double  carbonate  of  magnesium  and  cal- 
cium. The  last-named  species  forms  whole  mount- 
ain ranges,  and  is  often  confounded  with  limestone. 
Some  of  its  varieties  resemble  marble.  Magnesium 
minerals  frequently  have  a  soapy  feeling,  as  in  soap- 
stone,  and  so  may  be  recognized  by  touch.  Salts 
of  magnesium  are  found  in  sea-water,  and  in  many 
mineral  springs. 

The  metal  itself  is  usually  prepared  by  heating 
the  chloride  with  sodium;  thus: 

MgCl3  +  Na2  =  Mg  +  2NaCl. 

It  is  bluish-white,  fusible  at  low  redness,  volatile  at 
higher  temperatures,  and  has  a  specific  gravity  of 
1.75.  It  is  easily  combustible,  and  burns  with  an  in- 
tensely brilliant  light,  emitting  dense,  white  smoke- 
clouds  of  its  solid  oxide,  MgO.  It  is  commonly  sold 
in  the  form  of  wire  or  ribbon,  and  may  be  kindled 
with  a  common  match.  Its  light  gives  a  continuous 
spectrum,  but  is  brightest  toward  the  violet  end, 
and  abounds  especially  in  those  rays  which  possess 
chemical  activity.  On  this  account  it  is  available 
for  photographic  purposes  ;  and  is  actually  so  used 
as  a  source  of  illumination  in  photographing  the  in- 
terior of  caverns. 

The  compounds  of  magnesium  are  quite  simple. 
The  oxide,  MgO,  also  known  as  magnesia,  is  a  white 
powder  somewhat  used  in  medicine.  Its  popular 
name  well  illustrates  a  common  method  of  abbrevi- 
ating the  names  of  oxides;  as,  for  example,  SiO2, 


224  INORGANIC  CHEMISTRY. 

silica  ;  Na2O,  soda  ;  K2O,  potassa  ;  BaO,  baryta  ; 
SrO,  strontia  ;  A12O8,  alumina,  etc.  The  superior 
convenience  of  these  names  over  such  terms  as 
silicon  dioxide,  barium  monoxide,  etc.,  is  evident. 
Magnesia  unites  readily  with  water  to  form  a 
hydroxide,  Mg(OH)2,  which  occurs  naturally  crys- 
tallized as  the  mineral  brucite.  The  carbonate, 
MgCO3,  is  also  found  as  a  mineral,  magnesite  ;  and, 
artificially  precipitated  in  union  with  hydroxide,  as 
the  magnesia  alba  of  pharmacy.  The  double  carbon- 
ate, MgCO3  +  CaCO3,  has  already  been  referred  to 
as  dolomite. 

The  most  important  salt  of  magnesium  is  the 
sulphate,  MgSO4,  7H2O.  It  was  originally  found  in 
a  spring  at  Epsom,  England  —  whence  the  common 
name  of  Epsom  salts.  It  is  now  prepared  by  treating 
either  magnesite  or  dolomite  with  sulphuric  acid, 
and  evaporating  the  solution  to  the  crystallizing 
point.  It  is  a  useful  reagent  in  chemical  analysis, 
and  is  a  common  household  medicine. 

The  water  of  crystallization  in  magnesium  sul- 
phate deserves  especial  study.  If  the  salt  be  heated 
to  about  120°  C.,  six  molecules  of  its  water  are  ex- 
pelled ;  but  the  seventh  molecule  is  retained  with 
great  tenacity  up  to  a  temperature  of  nearly  200°. 
This  molecule,  therefore,  is  differently  combined 
from  the  others,  and  is  known  as  water  of  constitu- 
tion. It  may  be  replaced  by  other  sulphates  ;  as, 
for  example,  K2SO4,  yielding  the  double  sulphate 
MgSO4,  K2SO4,  6H2O. 

'' 


This  compound  is  the  type  of  an  important  class  of 
double  salts  which  result  from  the  union  of   the 


GLUCINUM,   MAGNESIUM,  ZINC,  ETC.      22$ 

alkaline  sulphates  with  the  sulphates  of  magnesium, 
zinc,  iron,  cobalt,  nickel,  and  copper.  These  salts 
show  that  there  is  some  relationship  between  mag- 
nesium and  the  last  four  metals. 

ZINC,  though  far  less  abundant  than  magnesium, 
is  more  familiar  as  a  metal.     It  is  found  in  many 


FIG.  49. — Zinc-Furnace. 

minerals ;  but  its  chief  ores  are  the  oxide,  zincite  ; 
the  sulphide,  zinc  blende ;  the  silicate,  calamine ; 
and  the  carbonate,  smithsonite.  These,  in  smelt- 
ing, are  first  roasted,  and  then  heated  in  either 
earthenware  tubes  or  fire-clay  crucibles  with  coke 
or  charcoal.  Zinc  is  set  free,  and  distilled  off  into 
suitable  vessels.  It  is  finally  remelted  and  cast  into 
bars,  which  are  known  commercially  as  spelter. 
Sometimes  the  zinc-vapor  is  condensed  in  the  form 
of  zinc-dust,  which  is  of  use  in  some  of  the  opera- 
tions of  organic  chemistry.  A  mixture  of  zinc-dust 
and  sulphur  may  be  used  to  illustrate  chemical 


226  INORGANIC  CHEMISTRY. 

union,  as  in  Experiment  i.  It  can  be  kindled  with 
a  match  and  burns  almost  like  gunpowder,  leaving 
a  residue  of  yellowish-white  sulphide. 

Zinc  is  a  bluish-white  metal  of  atomic  weight 
65,  and  a  specific  gravity  from  6.8  to  7.3.  It  melts 
at  423°,  and  boils  at  1,035°.  It  is  slightly  combus- 
tible, especially  in  thin  sheets,  and  burns  with  a 
greenish  flame.  At  ordinary  temperatures  it  is 
brittle ;  but  at  125°  to  150°  it  is  malleable,  and  may 
be  rolled  into  sheets.  At  205°  it  again  becomes 
brittle,  and  may  be  pulverized  in  a  mortar.  It  is 
largely  used  as  sheet-zinc,  for  fire-screens,  roofing, 
etc. ;  and  it  forms  the  positive  plate  in  all  voltaic 
battc  ies.  Brass  is  an  alloy  of  zinc  and  copper,  and 
German  silver  consists  of  zinc,  nickel,  and  cop- 
per. The  so-called  galvanized  iron,  used  for  roof- 
ing, cornices,  window-caps,  water-pipe,  etc.,  is  mere- 
ly iron  which  has  been  dipped  in  melted  zinc,  and 
so  coated  with  the  latter.  Granulated  zinc  is  the 
most  convenient  form  of  zinc  for  laboratory  pur- 
poses ;  it  is  prepared  by  melting  zinc  in  an  iron 
ladle,  and  pouring  it  gradually  from  a  height  of 
about  two  metres  into  cold  water.  Other  fusible 
metals,  like  lead,  tin,  or  cadmium,  may  be  granu- 
lated in  the  same  way. 

Chemically,  the  compounds  of  zinc  resemble 
those  of  magnesium.  The  oxide,  ZnO,  is  white 
when  cold,  yellow  when  hot.  A  large  deposit 
of  it  occurs  at  Franklin  and  Sterling,  New  Jer- 
sey, in  red  masses  which  owe  their  color  to  man- 
ganese as  an  impurity.  The  pure  zinc  oxide  is 
important  as  a  white  paint,  which  is  not  discolored 
by  atmospheric  agencies.  Zinc  sulphide,  ZnS,  is 
often  produced  in  the  laboratory  as  a  white  precipi- 


GLUCINUM,  MAGNESIUM,  ZINC,  ETC.      227 

tate,  by  adding  ammonium  sulphide  to  a  solution  of 
any  soluble  zinc-salt.  It  occurs  in  nature  as  a  very 
common  crystalline  mineral,  but  is  generally  col- 
ored yellow,  brown,  or  black,  by  impurities.  The 
chloride,  ZnClg,  is  a  pasty  solid,  which  is  prepared 
by  dissolving  zinc  in  hydrochloric  acid  and  evapo- 
rating to  dryness.  It  is  used  in  surgery  as  a  caus- 
tic, and  by  tinners  for  cleansing  tin-plate  previous  to 
soldering.  It  is  also  used  on  a  large  scale  as  an  an- 
tiseptic, in  the  preservation  of  wood  from  decay. 
The  process,  which,  from  the  name  of  its  invent- 
or, is  called  Burnettizing,  consists  in  inclosing  the 
wood  in  strong  iron  cylinders,  pumping  out  the  air 
by  a  powerful  steam-pump,  and  then  allowing  the 
solution  of  zinc  chloride  to  flow  in  under  very 
heavy  pressure.  The  wood  is  thus  completely  per- 
meated by  the  preservative,  and  will  last  for  years 
without  rotting.  Copper  sulphate,  mercuric  chlo- 
ride, coal-tar,  creosote,  etc.,  are  also  applied  to  wood 
in  the  same  way  and  for  the  same  purpose. 

Zinc  sulphate,  ZnSO4,  ;H2O,  also  called  white 
vitriol,  resembles  magnesium  sulphate  very  closely. 
It  forms  similar  double  sulphates,  and  its  water  of 
crystallization  behaves  in  the  same  way.  Its  uses 
are  chiefly  medicinal,  although  in  large  doses  it  is 
poisonous.  Applied  externally  in  weak  solutions, 
it  quiets  local  inflammation ;  and  it  is  especially 
used  in  treating  diseases  of  the  eye.  Most  of  the 
so-called  "  eye-waters  "  are  merely  preparations  of 
zinc  sulphate. 

CADMIUM,  atomic  weight  112,  is  a  rare  metal 
which  is  chiefly  found  as  an  impurity  in  zinc.  It  is 
bluish-white,  brilliant,  and  of  specific  gravity  8.6. 
It  melts  at  320°  C.,  and  boils  at  860°,  forming  a  va- 


228  INORGANIC  CHEMISTRY. 

por  having  only  half  the  density  indicated  by  its 
atomic  weight.  Hence  its  molecule  consists  of  a 
single  atom.  Cadmium  is  used  in  making  certain 
fusible  alloys,*  and  in  preparing  a  few  compounds. 
The  iodide,  CdI2,  is  employed  to  some  extent  in 
photography ;  and  the  sulphide,  CdS,  is  a  brilliant 
yellow  precipitate  which  is  much  prized  by  artists 
as  a  pigment. 

MERCURY,  or  quicksilver,  being  the  only  metal 
liquid  at  ordinary  temperatures,  has  always  been  an 
object  of  both  popular  and  scientific  interest.  It  is 
found  in  nature  in  the  free  state,  and  also  in  several 
ores  ;  but  only  one  of  the  latter,  cinnabar,  HgS,  has 
any  practical  importance.  It  is  extensively  mined 
in  Spain,  Austria,  China,  Mexico,  and  Peru ;  but 
fully  two  thirds  of  the  whole  annual  mercury-yield 
of  the  world  comes  from  a  few  localities  in  Califor- 
nia. From  cinnabar  the  metal  is  easily  extracted 
by  a.  process  of  roasting  with  lime.  The  mercury 
volatilizes,  and  is  condensed  in  suitable  chambers 
or  pipes.  It  is  purified  by  straining  through  linen, 
and  is  sent  into  commerce  in  strong  bottles  made  of 
wrought-iron. 

The  specific  gravity  of  mercury,  at  o°,  is  13.596. 
At  —39.5°  it  solidifies  to  a  malleable  mass,  of  spe- 
cific gravity  14.19.  At  357°  it  boils,  yielding  a  vapor 
of  density  100,  its  atomic  weight  being,  as  in  the 
case  of  cadmium,  twice  as  great,  or  200.  Hence 
the  mercury  molecule  consists  of  one  atom.  Pure 
mercury  does  not  tarnish  in  the  air  until  heated 
above  300°,  when  it  slowly  unites  with  oxygen  to 
form  the  red  oxide.  It  combines  directly  with  chlo- 
rine, bromine,  iodine,  and  sulphur,  and  dissolves  in 

*  Described  under  bismuth. 


GLUCINUM,   MAGNESIUM,   ZINC,  ETC.      229 

nitric  and  hot  sulphuric  acids.  Its  symbol,  Hg,  is 
from  the  Latin  hydrargyrum.  It  is  used  in  making 
thermometers,  barometers,  and  other  physical  in- 
struments, in  silvering  mirrors,  in  the  manufacture 
of  many  medicinal  preparations,  and  in  extracting 
gold  and  silver  from  their  ores.  With  many  of  the 
metals  it  unites  easily,  forming  a  class  of  alloys 
called  amalgams.  In  handling  mercury  great  care 
should  be  taken  to  prevent  it  from  coming  in  con- 
tact with  gold  rings  or  other  jewelry,  on  account  of 
the  readiness  with  which  gold  amalgamates.  A 
bit  of  gold-leaf  will  dissolve  in  a  drop  of  quicksilver 
almost  instantaneously  (see  Experiment  100). 

Mercury  forms  two  sets  of  compounds,  which 
are  called  mercurous  and  mercuric  compounds  re- 
spectively. In  the  first  set,  which  are  unstable,  it 
seems  to  be  a  monad  ;  in  the  second  it  is  unmistak- 
ably bivalent.  The  following  are  its  more  impor- 
tant compounds  : 

Mercum:  oxide,  HgO,  is  the  well-known  red 
oxide  formed  by  heating  mercury  in  the  air.  At  a 
temperature  above  350°  it  gives  off  its  oxygen,  and 
is  noted  as  the  substance  from  which  that  gas  was 
first  obtained  pure  (see  Experiment  2,  and  Chapter 
IV).  Mercurous  oxide,  Hg2O,  is  black  and  unstable. 
Mercuric  sulphide,  HgS,  has  already  been  referred 
to  as  the  ore  cinnabar.  When  H2S  is  passed  into  a 
solution  of  a  mercuric  salt,  the  same  sulphide  is 
thrown  down  as  a  black  precipitate.  By  subliming 
a  mixture  of  mercury  and  sulphur  it  is  obtained  in 
a  bright-red  modification,  called  vermilion,  which 
is  used  as  a  scarlet  pigment. 

When  mercury  is  treated  with  nitric  acid  in 
quantity  insufficient  to  dissolve  the  whole  of  it, 


230  INORGANIC  CHEMISTRY. 

mercurous  nitrate,  HgNO8,  is  produced  in  white 
crystals.  With  an  excess  of  nitric  acid  the  mercu- 
ric salt,  Hg(NO8)2,  is  formed.  With  hot  sulphuric 
acid  mercury  yields  mercuric  sulphate,  HgSO4 ;  a 
compound  used  in  some  forms  of  galvanic  battery. 

The  chlorides  of  mercury,  HgCl  *  and  HgCl2, 
are  both  important.  Mercurous  chloride  is  a  white, 
insoluble  powder,  much  used  in  medicine  under 
the  familiar  name  of  calomel.  Mercuric  chloride, 
which  is  prepared  on  a  large  scale  by  subliming  a 
mixture  of  mercuric  sulphate  and  common  salt,  is 
soluble  in  water,  alcohol,  and  ether,  and  crystallizes 
easily.  It  is  the  well-known  violent  poison,  corro- 
sive sublimate.  The  best  antidote  for  this  poison 
is  white  of  egg,  administered  raw,  in  large  doses. 
The  albumen  of  the  egg  forms  an  insoluble  clot 
with  the  mercuric  chloride,  which  may  afterward  be 
removed  from  the  stomach  by  means  of  an  emetic. 

Both  of  the  mercury  iodides  are  employed  me- 
dicinally. The  mercurous  compound  is  green  ;  the 
mercuric  salt  is  bright  scarlet.  The  properties  of 
the  latter  substance  are  so  extraordinary  that,  al- 
though they  were  partly  brought  out  in  Experi- 
ment 3,  they  deserve  further  experimental  atten- 
tion here. 

EXPERIMENT  86. — Dissolve  in  water,  in  separate 
vessels,  nine  parts  of  mercuric  chloride  and  eleven  of 
potassium  iodide.  Mix  the  two  colorless  solutions, 
and  a  heavy  precipitate,  yellow  at  first,  scarlet  after- 
ward, will  form.  Shake  vigorously  and  divide  into 

TT         /"M 

*  Many  chemists  write  this  HgaCla,  or    t  •         regarding  mercury 

Hg-Cl, 

as  invariably  dyad.  Good  arguments  can  be  cited  in  favor  of  either 
formula. 


GLUCINUM,  MAGNESIUM,   ZINC,   ETC.      231 

three  portions.  To  one  portion  add  an  excess  of 
mercuric  chloride  solution,  and  to  the  second  por- 
tion an  excess  of  potassium  iodide.  In  each  case 
the  precipitate  will  redissolve,  leaving  the  fluid 
colorless.  Filter  the  third  portion,  and  wash  and 
dry  the  precipitate.  Heat  a  little  of  it  gently  on  a 
bit  of  porcelain  or  a  slip  of  glass,  and  it  will  change 
from  scarlet  to  bright  yellow.  On  cooling,  it  will 
pass  slowly  back  to  its  original  color.  Under  the 
microscope  this  change  is  very  beautiful,  inasmuch 
as  the  scarlet  may  be  seen  to  leap  from  particle  to 
particle  of  the  yellow  powder. 

These  color-changes  are  due  to  the  fact  that 
mercuric  iodide  exists  in  two  distinct  modifica- 
tions, having  different  optical  properties  and  differ- 
ent crystalline  form.  In  Experiment  3  we  have  an 
example  of  dry  double  decomposition,  which  is  one 
of  the  very  rarest  of  chemical  phenomena. 


n 


CHAPTER  XXV. 

THE  ALUMINUM   GROUP. 

ALUMINUM,  as  regards  abundance,  may  be 
ranked  side  by  side  with  sodium,  calcium,  and 
magnesium.  It  enters  into  the  composition  of  all 
the  important  primitive  rocks,  and  all  slates  and 
clays  consist  mainly  of  its  silicates.  In  the  crust  of 
the  earth,  only  oxygen  and  silicon  occur  in  larger 
quantities. 

The  metal  itself  is  prepared  by  passing  the  va- 
por of  a  double  chloride  of  aluminum  and  sodium 
over  metallic  sodium.  Sodium  chloride  is  formed, 
and  metallic  aluminum  is  set  free.*  It  is  a  tin-white 
metal,  brilliant,  malleable,  and  ductile,  and  has  a 
specific  gravity  of  2.583.  It  fuses  at  about  850°,  and 
is  an  excellent  conductor  of  heat  and  electricity. 
It  does  not  tarnish  in  the  air,  it  is  easily  worked, 
and  it  combines  the  properties  of  lightness  and 
strength  to  an  extraordinary  degree.  If  it  could- 
only  be  produced  cheaply  from  common  clay,  it 
would  be  one  of  the  most  useful  of  metals.  Indeed, 
it  has  been  called  "the  metal  of  the  future,"  al- 
though at  present  it  is  only  employed  for  a  very 
few  purposes.  An  alloy  of  ten  parts  of  aluminum 

*  Several  modified  processes   for  the  manufacture  of  aluminum 
have  recently  been  patented  in  England. 


THE  ALUMINUM  GROUP.  233 

with  ninety  of  copper  is  known  as  aluminum  bronze, 
and  is  a  dangerous  imitation  of  gold.  It  is  some- 
what used  in  fine  philosophical  instruments. 

Aluminum  is  trivalent,  and  has  an  atomic  weight 
of  27.  It  forms  one  set  of  compounds,  of  which  the 
oxide,  alumina,  A12OS,  is  the  type.  Such  oxides  as 
A12O3,  Fe2O3,  Cr2O3,  and  Mn2O3,  are  termed  sesqui- 
oxides. 

Alumina  occurs  crystallized  in  nature  as  the 
mineral  corundum,  and  is  usually  colored  by  im- 
purities. The  yellow  variety  is  called  "  Oriental 
topaz  "  ;  the  purple  is  the  "  Oriental  amethyst "  ;  the 
green  is  the  "  Oriental  emerald."  The  sapphire  is 
merely  blue  corundum,  and  the  ruby  is  a  red  vari- 
ety. These  gems  can  now  be  produced  artificially. 
Emery,  which  is  so  important  as  a  polishing-pow- 
der,  is  an  impure  corundum. 

Aluminum  forms  several  hydroxides,  the  com- 
pound A12(OH)6  being  the  most  characteristic. 
When  artificially  precipitated,  as  by  the  addition 
of  ammonia  to  an  aluminum  salt,  they  possess  the 
property  of  uniting  with  organic  dye-stuffs  to  form 
insoluble  substances  called  "  lakes."  Aluminum  hy- 
droxide, therefore,  plays  an  important  part  in  the 
processes  of  dyeing,  being  thrown  down  in  the  fiber 
of  the  cloth  for  the  purpose  of  fixing  and  retaining 
colors. 

EXPERIMENT  87. — Dissolve  a  crystal  of  alum  in 
water,  and  add  ammonia  to  the  solution.  Warm, 
and  filter  off  the  insoluble,  gelatinous  A12(OH)6 
which  is  precipitated.  Now  pour  over  the  precipi- 
tate a  solution  of  logwood  or  cochineal.  The  color 
will  be  retained  and  can  not  be  washed  out. 

In  alumina  we  have  an  oxide  which  may  play 


234  INORGANIC  CHEMISTRY. 

the  part  of  either  an  acid-former  or  a  base.  With 
strong  acids  it  forms  characteristic  salts,  like  the 
sulphate ;  and  with  strong  bases  it  unites  to  pro- 
duce aluminates. 

EXPERIMENT  88. — To  a  solution  of  alum  add  a 
very  little  caustic  potash  or  caustic  soda.  A  pre- 
cipitate of  hydroxide  will  be  thrown  down,  which 
will  be  redissolved  upon  the  addition  of  more  alkali. 
Metallic  aluminum  itself  may  be  dissolved,  with  evo- 
lution of  hydrogen,  by  potassium  or  sodium  hydrox- 
ide. In  these  reactions  potassium  or  sodium  alumi- 
nate  is  formed. 

The  most  important  simple  salt  of  aluminum  is 
the  sulphate,  A12(SO4)3,  i8H2O.  It  is  much  used  by 
dyers  as  a  mordant ;  and  an  impure  variety  of  it 
occurs  in  commerce  under  the  name  of  alum-cake. 
It  combines  with  the  sulphates  of  the  alkaline  met- 
als to  form  a  class  of  double  salts  known  as  alums, 
of  which  potassium  alum,  K2SO4,  A12(SO4)3,  24H2O,  is 
the  commonest  example.  The  formula  of  this  salt 
may  be  halved,  and  written  KA1(SO4)2,  I2H2O;  or, 
structurally— 

A1^So!-KI2Haa 

With  ammonium  sulphate,  ammonium  alum  is 
formed ;  and  so  also  we  may  put  either  Na,  Ag,  Tl, 
Cs,  or  Rb  in  place  of  K,  or  Cr,  Ga,  In,  Fe,  or  Mn  in 
place  of  Al.  In  every  case  we  shall  have  a  salt  con- 
taining twelve  molecules  of  water,  and  crystallizing 
in  regular  octahedra ;  and  all  of  these  salts  may  be 
represented  by  the  general  formula — 

M'M^SO^a,  i2H2O, 

in  which  M1  stands  for  a  univalent  metal  and  Mia  for 
a  triad.  The  potassium  and  ammonium  aluminum 


THE  ALUMINUM  GROUP.  235 

alums  are  both  important,  and  are  used  as  mor- 
dants in  the  art  of  dyeing. 

In  the  mineral  kingdom,  in  addition  to  the  spe- 
cies already  mentioned,  we  find  a  number  of  highly 
interesting  aluminum  compounds.  The  turquoise 
is  an  aluminum  phosphate,  the  garnet  and  emerald 
are  silicates  containing  aluminum,  and  the  topaz 
is  a  compound  which  may  be  represented  by  the 
formula  Al2SiO4F2.  Another  substance  of  special 
interest  is  cryolite,  a  double  fluoride  of  aluminum 
and  sodium,  6NaF,  A12F6,  which  forms  a  vast  bed  in 
Western  Greenland.*  Thousands  of  tons  of  this 
mineral  are  annually  brought  to  the  United  States, 
and  worked  over  by  a  special  process  so  as  to  yield 
aluminum  sulphate  and  an  excellent  quality  of  soda- 
ash.  A  kind  of  glass  which  outwardly  resembles 
porcelain  is  also  made  by  fusing  cryolite  with  sand. 

A  beautiful  blue  ornamental  stone,  lapis  lazuli, 
is  a  silicate  of  aluminum  and  sodium  containing  sul- 
phur. Formerly  its  powder  was  used  by  artists  as 
a  paint,  under  the  name  of  ultramarine  ;  but  at  pres- 
ent this  substance  is  produced  artificially  from  very 
cheap  materials.  First,  a  mixture  of  clay  with  so- 
dium sulphate,  soda,  charcoal,  and  sulphur,  is  heated 
in  crucibles,  and  a  valuable  paint  known  as  green 
ultramarine  is  obtained.  This,  reheated  with  sul- 
phur, yields  blue  ultramarine,  which  is  much  used 
for  water-colors  and  for  paper-staining.  In  1829 
ultramarine  was  worth,  in  England,  sixty  dollars 
a  pound  ;  to-day  its  price  is  about  twelve  cents. 
Nearly  twenty  million  pounds  are  annually  made. 
Violet  and  red  ultramarines  have  also  been  pre- 

*  Cryolite  has  recently  been  discovered  near  Pike's  Peak,  in  Colo- 
rado. 


236  INORGANIC  CHEMISTRY. 

pared ;  but  to  none  of  these  compounds  can  abso- 
lutely definite  chemical  formulas  as  yet  be  as- 
signed. 

Pottery  and  porcelain,  being  made  from  clay, 
are  more  or  less  impure  silicates  of  aluminum. 
Red  bricks  and  red  pottery  owe  their  color  to  con~u 
pounds  of  iron ;  and  fire-clay,  from  which  the  fire- 
brick linings  of  furnaces  are  made,  contains  large 
admixtures  of  silica.  Porcelain  differs  from  glass 
in  being  non-transparent,  or  at  best  only  translu- 
cent, and  exceedingly  infusible. 

Pure  porcelain-clay  or  kaolin  is  a  hydrous  alumi- 
num silicate,  H2Al2Si2O8  -f  H2O.  It  is  derived  from 
rocks  containing  feldspar  (K2Al2Si6O16),  by  the  atmos- 
pheric process  known  as  weathering.  When  it  is 
baked  in  an  appropriate  furnace,  it  loses  water  and 
hardens,  and  a  porous  mass  is  produced.  In  mak~ 
ing  porcelain  the  finely-powdered  kaolin  is  mixed 
with  water  to  a  very  thick  paste,  and  then  molded 
into  the  desired  shape.  A  little  feldspar,  chalk,  or 
gypsum  is  also  added  to  the  clay,  in  order  to  form 
a  fusible  silicate  in  quantity  just  sufficient  to  bind 
the  particles  of  the  ware  firmly  together.  Upon 
firing,  as  the  process  of  burning  is  called,  a  porous 
"  biscuit-ware  "  is  obtained,  which  is  afterward  sub- 
jected to  a  process  of  glazing.  For  the  finest  porce- 
lain the  glazing  material  is  generally  pure  feldspar, 
finely  powdered  and  mixed  with  water  to  a  very 
thin  consistency  ;  into  this  the  biscuit  is  dipped,  and 
then  fired  over  again.  The  feldspar,  being  fusible, 
melts ;  and  a  thin,  smooth,  glassy  layer  covers  the 
surface  of  the  ware.  A  cheaper  glaze  for  common 
stone-china  consists  of  a  mixture  of  clay,  chalk, 
ground  flints,  and  borax ;  but  many  other  recipes 


THE  ALUMINUM  GROUP,  237 

are  also  used.  Earthenware  is  generally  salt-glazed, 
a  process  which  consists  in  throwing  common  salt 
into  the  kiln  just  before  the  firing  is  finished.  The 
salt  volatilizes,  and  a  fusible  silicate  of  aluminum 
and  sodium  is  formed  all  over  the  surface  of  the 
pottery.  The  colors  used  in  decorating  porcelain 
consist  of  various  metallic  oxides ;  cobalt  oxide  for 
blue,  chromic  oxide  for  green,  etc.  Some  colors 
are  put  on  previous  to  glazing ;  but  the  more  deli- 
cate tints,  as  well  as  any  gilding,  are  imparted  in  a 
separate  firing  over  the  glaze. 

GALLIUM,  which  is  chemically  allied  to  alumi- 
num, is  an  excessively  rare  metal,  of  atomic  weight 
69.  It  was  discovered  in  1875,  and  is  interesting  as 
being  one  of  the  metals  of  which  the  existence  and 
properties  were  predicted  in  advance  of  actual 
discovery.  Its  specific  gravity  is  5.9,  and  it  melts 
at  30°  C.  It  becomes  liquid  in  the  heat  of  the 
hand  !  Its  oxide  is  Ga2O3,  and  its  sulphate  forms 
alums. 

INDIUM,  atomic  weight  113.5,  was  discovered  in 
1875.  Like  gallium,  it  is  exceedingly  rare.  The 
metal  has  a  specific  gravity  of  7.4,  and  outwardly 
resembles  zinc.  Its  sulphate  forms  an  alum.  Indi- 
um and  gallium  were  both  discovered  by  spectrum 
analysis,  and  both  are  trivalent. 

Scandium,  yttrium,  terbium,  erbium,  and  ytter- 
bium are  very  rare  metals  having  only  theoretical 
interest.  They  are  all  trivalent,  forming  sesqui- 
oxides,  which  are  strong  bases.  The  existence  of 
scandium  was  predicted  by  Mendelejeff  in  advance 
of  its  actual  discovery  by  Nilson. 

Cerium,  lanthanum,  and  didymium  are  three 
other  rare  metals  which  usually  occur  associated 


238  INORGANIC  CHEMISTRY. 

together.  Lanthanum  is  a  triad,  cerium  a  tetrad, 
and  didymium  a  pentad.  With  didymium,  in  inti- 
mate admixture,  a  fourth  metal,  samarium,  has  re- 
cently been  detected.  Cerium  oxalate  has  a  limited 
use  in  medicine. 


CHAPTER   XXVI. 

THE   TETRAD    METALS. 

IN  addition  to  cerium,  which  was  mentioned  in 
the  preceding  chapter,  titanium,  zirconium,  tin, 
lead,  and  thorium  are  quadrivalent.  In  fact,  they 
may  all  be  classed  in  a  series  of  elements  of  which 
carbon  and  silicon  are  the  first  and  second  mem- 
bers. TITANIUM,  atomic  weight  50,  is  one  of  the 
rarer  metals.  Its  oxide,  TiO2,  is  a  natural  mineral, 
and  has  a  limited  application  in  giving  a  yellowish 
tint  to  porcelain.  Titanium  occurs  in  many  iron- 
ores,  and  renders  them  more  difficult  of  working. 
In  the  blast-furnace  it  sometimes  combines  with  ni- 
trogen and  carbon  so  as  to  form  a  nitrocyanide, 
Ti(CN)2  -f  3Ti3N2,  which  looks  strikingly  like  metal- 
lic copper.  ZIRCONIUM,  atomic  weight  90,  is  even 
rarer  than  titanium.  Like  alumina,  zirconia  (ZrO2) 
is  sometimes  basic  and  sometimes  acid-forming. 
The  mineral  zircon,  ZrSiO4,  is  used,  under  the  name 
of  hyacinth,  as  a  gem.  THORIUM,  atomic  weight 
232,  is  exceedingly  rare,  and  has  no  practical  impor- 
tance. Its  oxide  is  a  strong  base. 

TIN,  atomic  weight  118,  is  rarely  found  in  the 
metallic  state,  and  occurs  in  only  a  few  mineral 
species.  It  has  but  one  important  ore,  the  mineral 
cassiterite  or  tin-stone,  SnO2.  This  ore  varies  in 


240 


INORGANIC  CHEMISTRY. 


color  from  brown  to  black,  and  is  quite  heavy ;  but 
it  is  devoid  of  metallic  luster,  and  might  easily  be 
passed  over  as  valueless  by  an  untrained  observer. 
Tin  is  the  only  valuable  metal  which  has  not  as  yet 
been  found  in  paying  quantities  within  the  limits  of 
the  United  States.  It  is  chiefly  produced  in  Corn- 
wall, Borneo,  Malacca,  and  the  Island  of  Banca. 
Banca  tin  is  almost  chemically  pure,  while  English 
tin  always  contains  a  little  iron  and  lead. 

Tin  is  easily  extracted  from  its  ore  by  heating 
the  crushed  mineral  with  coal  or  charcoal  in  a  rever- 
beratory  furnace. 

SnOa  +  C  =  Sn  +  COa. 

It  is  a  white  metal,  of  specific  gravity  7.3,  and  a 
melting-point  of  235°.  Melted  tin  rea'dily  absorbs 
oxygen  from  the  air,  and  becomes  converted  into 
a  white  oxide,  SnO2.  When  a  bar  of  tin  is  bent,  it 
emits  a  peculiar  crackling  sound,  called  the  "  tin- 
cry,"  which  is  caused  by  the  friction  against  each 
other  of  interlaced  crystals.  The  crystalline  char- 
acter of  the  metal  may  be  rendered  evident  to  the 
eye  by  washing  the  surface  of  a  piece  of  tin-plate 
with  warm  dilute  nitro-hydrochloric  acid.  Crystal- 
line markings  will  presently  appear.  Tin  is  ductile, 
but  not  tenacious ;  it  is  also  highly  malleable,  and 
is  therefore  much  used  in  the  form  of  foil.  The 
cheaper  grades  of  tin-foil  are  adulterated  with  lead. 
Tin-plate,  or  sheet-tin,  is  really  tinned  iron. 
Sheets  of  rolled  iron,  chemically  clean,  are  dipped 
into  melted  tin,  and  acquire  a  coating  of  the  latter. 
Ordinary  mirrors  are  covered  with  an  amalgam 
of  tin  and  mercury ;  bronze  is  an  alloy  of  copper 
and  tin ;  plumber's  solder  consists  of  tin  and  lead, 


THE    TETRAD  METALS. 


241 


and  Britannia-metal  is  composed  mainly  of  tin  and 
antimony. 

The  symbol  of  tin,  Sn,  is  from  the  Latin  stan- 
num.  There  are  two  sets  of  tin  compounds,  which 
are  termed  stannous  and  stannic  compounds  respect- 
ively. Stannous  oxide,  or  tin  monoxide,  SnO,  is 
basic,  and  from  it  a  well-defined  series  of  salts  may 
be  derived.  Stannic  oxide,  or  tin  dioxide,  SnO2,  is 
weakly  basic  with  strong  acids,  and  weakly  acid 
with  strong  bases.  Sodium  stannate,  Na2SnO8, 
3H2O,  is  an  important  mordant  in  calico-printing. 
Stannous  chloride,  SnCl2,  2H2O,  and  stannic  chlo- 
ride, SnCl4,  5H2O,  are  also  much  used  as  mordants. 
The  anhydrous  stannic  chloride,  SnCl4,  is  a  volatile 
liquid  ;  but  its  hydrate  is  a  crystalline  salt.  Stan- 
nic sulphide,  SnS2,  forms  golden  scales  which  are 
used  for  bronzing  plaster  casts.  Its  commercial 
name  is  "mosaic  gold."  The  close  analogy  be- 
tween tin  and  other  members  of  the  same  group  is 
shown  by  the  subjoined  formulae : 


CO 

SnO 

CO, 

SiO, 

Ti02 

SnO* 

ecu 

SiCU 

TiCh 

SnCl4 

NaaCO3 

NaaSiOa 

NaaTiO3 

NaaSnOs 

LEAD,  although  classed  with  the  tetrads,  is  in 
most  of  its  compounds  bivalent,  and  might  fairly 
be  put  in  the  same  group  with  calcium  and  barium. 
In  chemical  structure  its  commoner  salts  resemble 
those  of  the  latter  metals ;  but  in  certain  organic 
compounds  it  is  unmistakably  quadrivalent. 

The  carbonate,  sulphate,  phosphate,  and  arsen- 
ate  of  lead  all  occur  in  nature  as  well-defined,  crys- 


242  INORGANIC  CHEMISTRY. 

tallized,  mineral  species  ;  but  the  only  ore  of  lead 
having  much  practical  importance  is  the  sulphide, 
PbS,  which  is  commonly  known  as  galena.  This 
ore  is  easily  reduced  by  heating  in  a  reverberatory 
furnace,  as  follows  :  First,  it  is  roasted  with  free  ac- 
cess of  air,  when  a  portion  is  oxidized  to  a  sulphate, 
PbSO4,  and  another  to  oxide,  PbO,  while  a  third 
part  remains  unchanged.  At  the  proper  time  the 
air  is  excluded  and  the  temperature  is  raised  ;  sul- 
phur dioxide  is  given  off,  and  lead  is  left  behind,  in 
accordance  with  the  subjoined  equations.  Both  re- 
actions occur  simultaneously  : 

PbSO4  +  PbS  =  2Pb  +  2SO3. 
2PbO  +  PbS  =  3Pb  +  SO3. 


In  actual  working  a  little  lime  is  added  in  order  to 
form  a  fusible  slag  with  the  impurities  of  the  ore. 
In  many  cases  the  lead  contains  some  silver,  which 
is  afterward  extracted  by  the  process  described  in 
the  chapter  upon  that  metal. 

Lead  is  a  bluish-white  metal,  of  atomic  weight 
207,  and  specific  gravity  11.38.  It  melts  at  332°, 
and  at  ordinary  temperatures  is  soft  enough  to  be 
scratched  by  the  finger-nail.  When  freshly  cut  it 
has  a  brilliant  metallic  luster;  but  it  quickly  tar- 
nishes on  the  surface  and  becomes  dull.  It  is  mal- 
leable and  ductile,  but  its  tenacity  is  so  slight  that 
it  is  not  available  for  wire  or  for  very  thin  foil. 
The  symbol,  Pb,  is  from  the  Latin  plumbum. 

The  salts  of  lead  are  all  poisonous  ;  and  hence  it 
is  often  an  important  matter  to  determine  whether 
or  not  leaden  water-pipes  affect  drinking-water  in- 
juriously. Even  the  slightest  traces  of  lead,  taken 
day  by  day  into  the  system,  will  in  time  accumulate 


THE   TETRAD  METALS.  243 

so  as  to  cause  very  serious  illness.  Perfectly  pure 
water,  free  from  air,  does  not  attack  lead ;  but  wa- 
ter containing  air  corrodes  it  slowly.  Drinking- 
waters  all  contain  salts  in  solution,  and  these  vary 
with  different  localities  and  different  sources  of  sup- 
ply. Hard  water,  or  water  carrying  either  sul- 
phates or  carbonates  dissolved  in  it,  soon  forms  a 
thin,  insoluble  coating  on  the  surface  of  lead  pipe, 
and  protects  it  from  further  action.  Such  waters, 
therefore,  are  relatively  safe.  On  the  other  hand, 
water  containing  nitrates,  chlorides,  or  free  car- 
bonic acid,  will  gradually  take  lead  into  solution, 
and  consequently  may  become  unwholesome  by 
contact  with  that  metal.  In  using  lead  pipes  the 
safest  rule  is  never  to  drink  water  which  has  been 
long  standing  in  them.  Always  allow  the  water  to 
run  until  it  flows  relatively  fresh  from  the  cistern 
or  water-mains.  If  water  is  suspected  of  containing 
lead,  the  impurity  may  be  detected  by  adding  a 
few  drops  of  hydrochloric  acid  and  passing  into 
it  a  current  of  sulphuretted  hydrogen.  If  lead  is 
present,  a  brownish  tinge  will  be  produced,  which 
may  best  be  observed  by  looking  through  a  very 
thick  layer  of  the  liquid.  With  much  lead  in  a  so- 
lution, sulphuretted  hydrogen  yields  a  heavy  black 
precipitate. 

Lead  forms  a  number  of  important  compounds, 
in  most  of  which  it  plays  the  part  of  a  dyad.  For 
example,  there  are  the  sulphate,  PbSO4 ;  a  nitrate, 
Pb(NO3)2 ;  a  chloride,  PbCl2,  etc.  The  acetate,  or 
sugar  of  lead,  will  be  described  under  acetic  acid, 
and  the  chromate,  chrome-yellow,  belongs  in  the 
chapter  with  chromium.  With  oxygen  lead  com- 
bines in  three  proportions,  forming  a  monoxide, 


244  INORGANIC  CHEMISTRY. 

PbO  ;  a  dioxide,  PbO2,  and  the  compound  known 
as  red-lead  or  minium,  Pb3O4.     The  last  may  be  re-  * 
garded  as  a  double  oxide,  2  PbO  +  PbO2. 

Lead  monoxide,  or  litharge,  is  a  yellowish  pow- 
der which  is  formed  whenever  lead  is  heated  with 
free  access  of  air.  It  is  a  strong  base,  and  combines 
freely  with  most  acids.  It  is  very  largely  used  as 
an  ingredient  of  flint-glass,  which  contains  a  color- 
less lead  silicate ;  it  is  also  employed  in  glazing 
earthenware,  in  preparing  other  lead  compounds, 
and  in  medicine.  The  dioxide  is  a  dark-brown 
powder  having  powerful  oxidizing  properties.  Red- 
lead  is  made  by  heating  litharge  for  several  hours 
to  dull  redness,  and  forms  a  valuable  paint.  It  is 
also  used  by  the  glass-makers,  and  in  the  prepara- 
tion of  some  cements. 

One  of  the  most  important  compounds  of  lead 
is  the  basic  carbonate,  2PbCO3,  Pb(OH)2,  which 
constitutes  the  valuable  paint  known  as  white-lead. 
This  may  be  prepared  by  several  processes,  the  old 
"  Dutch  method  "  being  the  best.  Spiral  coils  of 
sheet-lead  are  put  in  earthen  pots  with  a  little  vine- 
gar, and  exposed  for  several  weeks  to  the  slow  action 
of  carbon  dioxide  generated  by  the  fermentation 
of  spent  tan-bark  or  sawdust.  First,  a  layer  of  the 
bark  is  put  down,  and  on  this  the  earthen  pots  are 
arranged  in  rows,  covered  with  boards.  On  these 
another  layer  of  bark  is  spread,  then  a  second  series 
of  pots,  and  so  on  until  many  successive  layers  are 
arranged.  The  entire  pile  is  finally  covered  with 
spent  tan.  After  the  proper  lapse  of  time  the  lead  is 
found  to  be  converted  into  white-lead,  which  is  thor- 
oughly washed,  dried,  and  ground  up  with  linseed- 
oil.  It  is  often  adulterated  with  barium  sulphate. 


THE   TETRAD  METALS.  245 

Although  white-lead  is  by  far  the  most  brilliant 
of  the  white  paints,  it  is  subject  to  some  objections. 
It  is  readily  blackened  by  sulphuretted  hydrogen, 
and  it  is  poisonous  to  the  workmen  who  handle  it. 
House-painters  are  often  subject  to  the  painful  dis- 
ease known  as  lead-colic,  which  is  caused  by  the 
slow  absorption  of  small  particles  of  white-lead  into 
the  system.  Baryta-white  and  zinc-white  are  less 
beautiful  than  white-lead,  but  they  do  not  blacken 
and  they  are  not  unwholesome. 

From  solutions  containing  lead  the  metal  is  easily 
thrown  down. 

EXPERIMENT  89. — Suspend  a  rod  or  strip  of  zinc 
in  a  solution  of  lead  acetate.  In  the  course  of  a  few 
hours  the  zinc  will  be  covered  with  brilliant  me- 
tallic spangles  of  lead,  forming  what  is  called  the 
"  lead-tree."  For  every  atom  of  lead  thrown  down, 
one  atom  of  zinc  goes  into  solution.  If  the  process 
be  continued  long  enough,  all  the  lead  will  separate 
out,  and  zinc  acetate  will  remain  dissolved  : 

Pb(C2H302)a  +  Zn  =  Zn(CaH303)3  +  Pb. 

Similarly,  metallic  mercury,  placed  in  a  solution  of 
silver  nitrate,  will  precipitate  metallic  silver,  and  be 
itself  dissolved  ;  copper  will  precipitate  mercury ; 
iron  or  zinc  will  throw  down  copper,  and  so  on. 
With  each  pair  of  metals  the  one  which  is  precipi- 
tated is  electro-negative  to  the  one  which  displaces 
it  from  solution.  The  more  electro-positive  a  metal 
is,  the  stronger  will  be  its  affinity  for  acids. 


CHAPTER  XXVII. 

THE  ANTIMONY   GROUP. 

IN  the  same  natural  group  of  elements  with  ni- 
trogen, phosphorus,  and  arsenic,  we  find  the  metals 
vanadium,  antimony,  and  bismuth.  Each  of  these 
substances,  like  phosphorus,  may  act  either  as  a 
triad  or  a  pentad,  and  each  is  clearly  related  to  the 
others  through  a  regular  gradation  of  properties. 
This  is  indicated  in  the  following  table  of  atomic 
weights,  specific  gravity,  and  formulae : 


Nitrogen  . 

Atomic 
weight. 

Specific 
gravity. 

N2O3 

N2OB 

HNO3 

Phosphorus  
Vanadium. 

31 

ci  c 

1.837 

(j.;oo 

P203 
V2O3 

P205 
V2O6 

HPOs 
HVO3 

H3P04 
H3VO4 

Arsenic  

7C 

15.700 

As2O3 

As2O6 

H8AsO4 

Antimony  .     ... 

1  2O 

6.7O2 

Sb2O3 

Sb2O6 

HSbO3 

Bismuth    

208 

0.823 

Bi2O3 

Bi-zOs 

HBiO3 



If  we  consider  the  series  of  compounds  begin- 
ning with  nitric  acid,  we  shall  find  that  what  may 
be  called  the  chemical  intensity  decreases  as  we 
ascend.  Nitric  acid  is  a  very  strong  acid  ;  phos- 
phoric acid  is  a  little  weaker ;  and  so  on,  until  we 
reach  bismuthic  acid,  HBiO3,  which  is  exceedingly 
feeble.  In  general,  bismuth  is  a  basic  metal,  and 


THE  ANTIMONY  GROUP.  247 

antimony  may  act  either  as  an  acid-former  or  as  a 
base. 

VANADIUM,  although  traces  of  it  occur  widely- 
diffused  in  many  rocks,  is  one  of  the  very  rare  met- 
als. Until  quite  recently  its  compounds  had  no 
practical  applications  whatever,  but  now  they  are 
rapidly  coming  into  use  for  the  preparation  of  a 
very  fine  black  ink,  and  in  dyeing  with  aniline 
black.  Vanadic  acid  behaves  like  arsenic  and  phos- 
phoric acids,  and  forms  a  similar  variety  of  salts. 
Like  nitrogen,  vanadium  forms  five  oxides — V2O, 
VO,  V208,  V02,  and  V2O5. 

ANTIMONY,  although  not  widely  diffused,  is  nev- 
ertheless quite  abundant  in  some  localities,  and  ranks 
commercially  as  one  of  the  cheaper  metals.  It  is 
found  as  native  antimony,  as  sulphide,  Sb2S8,  as 
oxides,  and  in  a  variety  of  other  mineral  species. 
Some  of  the  more  important  silver-ores  are  double 
sulphides  containing  antimony. 

The  metal  is'  easily  obtained  from  its  sulphide 
by  heating  the  latter  with  scrap-iron.  It  melts  at 
450°  C.,  and  at  a  red  heat  is  volatile.  The  vapor 
oxidizes  easily  in  the  air,  and  forms  dense  white 
clouds  of  Sb2O3.  In  color,  antimony  is  bluish  white, 
and  in  texture  it  is  highly  crystalline.  It  is  so 
brittle  that  it  may  readily  be  pulverized  in  a  mor- 
tar. An  allotropic  variety  of  it,  which  is  obtained 
by  electrolysis,  is  curiously  explosive  when  either 
scratched  or  heated.  The  symbol,  Sb,  is  from  stib- 
ium. Metallic  zinc  precipitates  antimony  from  its 
solutions  as  a  black  powder,  which,  under  the  name 
of  antimony  black,  is  used  for  giving  to  plaster 
casts  the  appearance  of  steel. 

Antimony  is  chiefly  useful  in  its  alloys.     Type- 


248  INORGANIC  CHEMISTRY. 

metal  is  an  alloy  of  antimony,  lead,  and  tin,  in 
proportions  which  vary  with  different  makers.  In 
solidifying  from  the  fused  state,  type-metal  expands, 
insuring  an  accurate  copy  of  the  type-mold.  Lead, 
alone,  contracts,  and  can  not  give  sharp  castings. 
The  tin  toughens  the  alloy,  the  antimony  imparts 
the  necessary  hardness.  Britannia-metal  has  al- 
ready been  referred  to  as  composed  of  antimony 
and  tin ;  and  Babbit's  anti-friction  metal,  which  is 
used  by  machinists,  contains  antimony,  lead,  tin, 
and  a  little  copper. 

Antimony  hydride,  orantimoniuretted  hydrogen, 
SbH3,  is  a  colorless  gas  resembling  the  correspond- 
ing arsenic  compound.  Its  properties  were  suffi- 
ciently indicated  under  Experiment  77,  and  its  forma- 
tion affords  a  meansof  detecting  antimony  in  analysis. 

With  oxygen,  antimony  forms  three  oxides — 
Sb2Os,  Sb2O4,  and  Sb2O5.  From  the  trioxide,  by 
union  with  water,  ortho-antimonious  acid,  H8SbO3, 
and  meta-antimonious  acid,  HSbO2,  are  derived ; 
and  in  a  similar  way  the  pentoxide  yields  antimonic 
acid,  HSbO8.  These  acids  are  very  weak,  and  their 
salts  are  unimportant.  There  are  still  other  salts 
in  which  antimony  is  basic ;  and  one  compound  of 
this  kind,  a  tartrate  of  potassium  and  antimony,  is 
used  in  medicine  under  the  name  of  tartar  emetic. 
The  chlorides  of  antimony,  SbCl3  and  SbCl5,  are 
easily  formed  by  the  direct  union  of  the  metal 
with  chlorine.  The  first  is  a  pasty  solid,  sometimes 
called  "  butter  of  antimony  " ;  the  second  is  liquid 
and  volatile. 

The  sulphides  of  antimony,  Sb2S8  and  Sb2S5,  are 
both  interesting.  Like  the  similar  compounds  of 
arsenic,  they  form  sulpho-salts  ;  thus : 


THE  ANTIMONY  GROUP.  249 


NaaS  +  SbaSa  =  2NaSbS2,  sodium  sulphantimonite. 
3Na3S  +  Sb2S5  =  2Na3SbS4,      "       sulphantimonate. 

The  trisulphide  is  the  important  ore  of  antimony, 
stibnite,  a  heavy  gray  mineral  of  brilliant  metallic 
luster.  In  powder  this  mineral  is  an  important  inr 
gredient  of  some  fire-work  mixtures.  There  is  also 
an  orange-colored  modification  of  the  same  sul- 
phide, which  is  easily  obtained  in  the  laboratory, 
thus: 

EXPERIMENT  90.  —  Dissolve  some  powdered  an- 
timony in  aqua  regia  (HNO8  +  HC1),  and  dilute  the 
solution  with  water  until  it  just  begins  to  turn  tur- 
bid. Divide  it  into  two  parts,  and  saturate  one 
with  a  stream  of  hydrogen  sulphide.  Filter  off  the 
orange-red  precipitate,  dry  it,  and  heat  gently  in  a 
glass  tube.  It  will  be  slowly  transformed  into  the 
black  modification,  thus  showing  the  relation  be- 
tween the  two.  To  the  second  part  of  the  solution 
add  ammonium  sulphide.  The  orange-colored  pre- 
cipitate will  at  first  form,  and  then,  upon  the  addi- 
tion of  more  ammonium  sulphide,  will  redissolve  ; 
this  action  being  due  to  the  production  of  am- 
monium sulphantimonite,  which  is  soluble.  Simi- 
lar experiments  may  be  performed  with  a  solution 
of  tartar  emetic  instead  of  the  antimony  solution 
above  described.  Nitric  acid  alone  will  convert 
antimony  into  a  white  oxide,  which  is  insoluble. 

The  difference  between  the  two  varieties  of 
antimony  sulphide  is  probably  due  to  a  different 
arrangement  of  atoms  in  the  molecule.  The  tri- 
oxide  is  also  dimorphous,  and  the  dimorphism 
in  each  case  may  be  rendered  clear  by  the  sub- 
joined structural  formulae,  in  which  antimony  is 
trivalent  : 


250  INORGANIC  CHEMISTRY. 

QK^O  Ox  QK  ^S  Sv 

')0        Sb-O^Sb          *>S        Sb^S-Sb 
SK0  X0/  Sb<S  ^^ 

A  red  paint,  antimony  cinnabar,  is  a  double  com- 
pound of  antimonious  oxide  and  sulphide.  Glass  of 
antimony,  which  is  used  for  imparting  a  yellow  tint 
to  glass  and  porcelain,  is  a  substance  produced  by 
fusing  together  the  oxide  and  the  sulphide. 

BISMUTH  is  less  abundant  than  antimony,  and  is 
found  in  comparatively  few  minerals.  The  oxide 
and  sulphide  occur  as  definite  natural  species,  but 
the  metal  itself  is  also  found  in  nature,  and  furnishes 
the  chief  supply  of  bismuth  to  commerce.  It  is  sim- 
ply melted  out  from  the  adherent  rocky  material, 
and  collected  directly  in  the  metallic  state. 

Bismuth  is  brilliant,  brittle,  and  reddish  white. 
It  melts  at  264°  C.,  and  on  solidifying  from  fusion 
it  expands,  increasing  about  -fa  in  volume.  It  crys- 
tallizes easily,  and  this  fact  has  already  been  indi- 
cated in  Experiment  65.  The  crystals  are  rhombo- 
hedral,  but  might  readily  be  mistaken  for  cubes, 
and  often  display  brilliant  iridescent  colors  on  the 
surface. 

Bismuth  is  useful  mainly  in  its  alloys  and  its 
compounds.  Its  alloys  are  remarkable  for  their 
low  fusibility,  and  several  of  them  melt  below  the 
boiling-point  of  water.  Rose's  alloy  consists  of 
one  part  lead,  one  part  tin,  and  two  parts  bismuth, 
and  melts  at  93.7°  C.  Wood's  alloy,  which  melts  at 
60.5°,  contains  four  parts  bismuth,  two  of  lead,  one 
of  tin,  and  one  of  cadmium.  These  alloys  expand 
remarkably  in  solidifying  from  fusion,  and  are  used 
in  making  casts  of  medals  and  coins.  A  plaster 
cast  is  first  made,  and  then  filled  with  the  fusible 


THE  ANTIMONY  GROUP.  251 

alloy,  which,  expanding,  fills  and  reproduces  every 
line.  Other  alloys  of  this  kind  serve  to  make  safety- 
plugs  for  steam-boilers.  When  the  boiler  gets  too 
hot,  the  plug  melts  and  the  steam  escapes  harmlessly. 

In  its  commoner  compounds  bismuth  may  be  re- 
garded as  trivalent  ;  and  in  most  of  its  salts  it  acts 
distinctly  as  a  base.  Thus  we  have  an  oxide,  Bi2O3, 
a  chloride,  BiCl3,  etc.  ;  and  such  salts  as  the  nitrate, 
Bi(NO3)3,  and  the  sulphate,  Bi2(SO4)3.  When  water 
is  added  in  large  quantity  to  a  solution  of  a  bismuth 
salt,  the  latter  is  decomposed,  and  a  basic  compound 
is  precipitated.  The  reaction  is  exceedingly  char- 
acteristic, and  is  applied  analytically  to  the  detec- 
tion of  bismuth. 

EXPERIMENT  91.  —  Dissolve  some  powdered  bis- 
muth in  a  little  nitric  acid,  and  divide  the  solution 
into  two  parts.  Leave  one  to  crystallize,  and  add  a 
considerable  quantity  of  water  to  the  other.  The 
first  portion  will  yield  crystals  of  bismuth  nitrate, 
Bi(NO3)3,  3H2O  ;  and  the  second  will  form  a  copious 
white  precipitate  of  the  basic  nitrate  or  subnitrate, 
Bi(OH)2NO3.  The  relation  of  these  compounds  to 
each  other  and  to  bismuth  hydroxide  may  be  ren- 
dered clear  by  formulas,  thus  : 

XOH  N03  NO, 

Bi-OH  Bi-NOs  '  Bi-OH 

XOH 


The  basic  nitrate  is  a  very  important  medicinal 
agent  in  the  treatment  of  bowel  disorders.  If 
water  be  added  to  the  chloride  of  bismuth,  BiCl3, 
a  similar  white  precipitate  will  be  formed  consist- 
ing of  bismuth  oxychloride,  BiOCl.  This  com- 
pound has  been  used  as  a  white  face-powder,  but 


252  INORGANIC  CHEMISTRY. 

is  decidedly  unwholesome.  With  sulphuretted  hy- 
drogen, bismuth  solutions  yield  a  black  precipi- 
tate of  bismuth  sulphide,  Bi2S3.  The  same  com- 
pound is  thrown  down  by  ammonium  sulphide,  and 
is  insoluble  in  an  excess  of  the  reagent. 

Two  other  very  rare  metals,  being  pentads, 
properly  belong  in  this  chapter.  They  are  colum- 
bium,*  atomic  weight  94,  and  tantalum,  atomic 
weight  182.  Their  chlorides,  CbCl5  and  TaCl5,  and 
their  oxides,  Cb2O5  and  Ta2O5,  are  characteristic 
compounds.  From  the  oxides,  columbic  and  tanta- 
lic  acids  are  derived,  and  salts  of  these  acids  ex- 
ist in  a  few  rare  minerals. 

*  Also  known  as  niobium.     The  name  columbium  has  priority. 


CHAPTER    XXVIII. 

THE   CHROMIUM   GROUP. 

JUST  as  the  metals  of  the  preceding  group  are 
classed  with  nitrogen  and  phosphorus,  so  the  metals 
of  this  group,  chromium,  molybdenum,  tungsten,  and 
uranium,  may  be  regarded  as  members  of  the  same 
elementary  series  with  oxygen  and  sulphur.  As 
metals  they  have  little  importance ;  but  in  many  of 
their  compounds  they  are  very  useful. 

CHROMIUM,  atomic  weight  52,  owes  its  name  to 
a  Greek  word  signifying  color,  and  several  of  its 
compounds  are  important  paints.  It  occurs  in  vari- 
ous minerals,  but  not  very  abundantly ;  its  chief  ore 
being  chromite,  FeCr2O4.  The  metal  itself  is  ob- 
tained with  great  difficulty,  is  almost  absolutely  in- 
fusible, and  has  a  specific  gravity  of  6.8 1.  It  forms 
several  distinct  sets  of  compounds. 

In  chromous  oxide,  or  chromium  monoxide,  CrO, 
chromium  appears  to  be  bivalent.  This  oxide  is 
basic,  and  forms  salts  which  are  very  unstable,  and 
rapidly  absorb  oxygen  from  the  air. 

Chromic  oxide  or  chromium  sesquioxide,  Cr2O8, 
is  the  most  stable  of  the  chromium  compounds.  It 
is  a  brilliant-green  powder,  which  is  used  in  giving 
a  green  color  to  glass  and  porcelain.  The  emerald 
owes  its  hue  to  traces  of  this  compound.  From  it 


254  INORGANIC  CHEMISTRY. 

as  a  base  many  salts  may  be  derived  ;  for  example, 
there  is  a  sulphate  Cr2(SO4)3,  a  chloride,  Cr2Cl6,  etc. 
The  chloride  forms  superb  violet-colored  scales. 
Like  aluminum  sulphate,  chromic  sulphate  forms 
alums,  of  which  common  chrome  alum,  KCr(SO4)2, 
I2H2O,  is  the  type.  This  may  be  obtained  in  violet- 
colored  octahedral  crystals  as  follows  : 

EXPERIMENT  92.  —  Dissolve  about  thirty  grammes 
of  potassium  pyrochromate  *  in  the  smallest  possible 
quantity  of  water,  add  forty  grammes  of  sulphuric 
acid,  largely  diluted,  and  boil  with  successive  addi- 
tions of  small  quantities  of  alcohol  until  the  original 
orange  color  of  the  solution  is  completely  changed 
to  green.  Upon  moderately  long  standing,  crystals 
of  chrome  alum  will  be  deposited.  The  reaction  in- 
volves the  reduction  of  the  highly  oxidized  chro- 
mate  to  the  lower  oxidation  of  the  chromic  salt.  At 
the  same  time,  the  alcohol,  which  serves  as  the  re- 
ducing agent,  is  itself  oxidized. 

Chromium  trioxide,  CrO8,  is  the  starting-point 
from  which  chromic  acid,  H2CrO4,  and  a  large  num- 
ber of  chromates  may  be  derived.  These  chromates 
and  the  trioxide  resemble  the  sulphates  and  sulphur 
trioxide  in  chemical  structure  :  f 

OT?  OT-T 

S0a  =  0  Cr03  =  0 


qn  /OK  rn/OK 

SOa\OK  Cr0a\OK 

i 

Chromium  trioxide  is  easily  obtained  from  any 
chromate  by  treatment  with  sulphuric  acid  ;  thus  : 
EXPERIMENT  93.  —  Add   strong  sulphuric  acid, 

*  Commonly  called  bichromate  of  potash. 
f  Refer  to  Chapter  XVI. 


THE  CHROMIUM  GROUP. 


255 


very  gradually,  to  a  strong  solution  of  potassium 
pyrochromate.  Heat  will  be  evolved ;.  and,  upon 
cooling,  superb  crimson  needles  of  the  trioxide  will 
be  deposited.  These  may  be  dried  by  draining  on 
a  porous  brick  or  tile,  but  should  not  be  brought 
in  contact  with  any  organic  matter.  Most  organic 
bodies  are  oxidized  by  them,  Cr2O3  being  simultane- 
ously formed.  In  Experiment  92  a  reaction  of  this 
kind  took  place,  which  may  be  further  illustrated 
by  dropping  strong  alcohol  upon  the  dry  trioxide. 
The  alcohol  will  be  ignited  by  the  heat  of  the  oxida- 
tion. The  aqueous  solution  of  chromium  trioxide 
is  yellow,  and  may  be  regarded  as  containing  chro- 
mic acid,  H2CrO4, 

(HaO  +  CrO3  =  H2CrO4). 

Nearly  all  of  the  chromates  are  either  red,  orange, 
or  yellow,  and  several  of  them  are  exceedingly  im- 
portant. 

Potassium  forms  three  chromates ;  the  first  one, 
K2CrO4,  being  the  normal  salt.  The  other  two  may 
be  represented  as  formed  from  this  by  the  addition 
of  one  and  two  molecules  of  CrO3  respectively,  as 
follow  : 

K2CrO4  -f  CrOs  =  K2Cr2O7,  potassium  pyrochromate. 
K2CrO4  +  2CrO3  =  KaCrsOie,       "        trichromate. 

Structurally,  the  three  salts  may  be  represented 
thus : 


/  OK  CrOa  \  r\ 


The  second  of  these  chromates,  the  dichromate 
or  pyrochromate,  is  by  far  the  most  important  of 

12 


256  INORGANIC  CHEMISTRY. 

all  the  compounds  of  chromium,  and  from  it  the 
others  are  prepared.  It  is  made  directly  from  chro- 
mite  (chrome  iron-ore)  by  roasting  the  finely  pow- 
dered mineral  in  a  strong  oxidizing  flame  with  po- 
tassium carbonate  and  a  little  lime.  Sometimes  salt- 
peter is  added  also.  The  roasted  mass  yields  with 
water  a  yellow  solution  of  monochromate ;  which, 
treated  with  a  quantity  of  sulphuric  acid  half  suffi- 
cient to  set  its  chromic  acid  free,  deposits,  on  cool- 
ing, superb  orange-red  crystals  of  the  desired  salt. 

Potassium  pyrochromate  is  largely  used  in  dye- 
ing and  calico-printing,  in  preparing  the  various 
chromium  paints,  as  an  oxidizing  agent  in  bleaching 
discolored  fats  and  oils,  and  in  certain  of  the  pro- 
cesses of  photography.  Paper  dipped  in  a  solution 
of  it  acquires  a  pale-yellow  tint,  but  becomes  brown 
on  exposure  to  light.*  A  film  of  gelatine  saturated 
with  the  salt  becomes  insoluble  wherever  it  has 
been  acted  on  by  light,  but  remains  soluble  in  its 
other  portions.  A  photograph,  therefore,  taken  on 
such  a  film,  may  be  made  to  stand  out  in  actual  re- 
lief by  simply  dissolving  away  the  unattacked  parts ; 
and  then  either  copied  in  electrotype  or  in  type- 
metal,  or  transferred  to  a  lithographic  stone.  This 
fact  is  the  basis  of  all  the  processes  of  photographic 
printing,  such  as  are  used  in  the  production  of  helio- 
types,  autotypes,  photo-lithographs,  etc.f 

Another  important  chromate  is  lead  chromate, 
or  chrome-yellow,  PbCrO4.  This  useful  paint  is 
prepared  by  mixing  solutions  of  lead  acetate  and 
potassium  pyrochromate,  and  filtering  off  the  bright- 

*  Repeat  Experiment  83,  using  K2CraO7  instead  of  AgNOs-     The 
print  may  be  rendered  permanent  by  thorough  washing  with  water. 
I  For  details,  see  Abney's  "  Treatise  on  Photography." 


THE  CHROMIUM  GROUP.  257 

yellow  precipitate.*  Boiling-  with  a  caustic  alkali 
converts  it  into  chrome-red,  PbCrO4,  PbO.  Chrome- 
orange  is  a  mixture  of  chrome-red  and  chrome-yel- 
low. 

MOLYBDENUM,  atomic  weight  96,  is  one  of  the 
rarer  metals.  Its  chief  ore  is  molybdenite,  MoS2, 
which  strongly  resembles  graphite  in  its  outward  ap- 
pearance. It  forms  complicated  compounds,  but  its 
leading  oxide,  MoO3,  and  molybdic  acid,  H2MoO4, 
are  analogous  to  the  corresponding  oxides  and  acids 
of  sulphur  and  chromium.  Ammonium  molybdate 
is  a  very  important,  practically  indispensable  re- 
agent, in  the  exact  analysis  of  iron-ores  and  ferti- 
lizers. 

TUNGSTEN,  atomic  weight  184,  is  somewhat  rare, 
though  more  abundant  than  molybdenum.  It  is 
found  in  several  minerals,  but  chiefly  in  a  tungstate 
of  iron,  wolfram,  FeWO4.  The  symbol,  W,  is  de- 
rived from  wolfram ;  but  the  name  of  the  metal 
itself,  of  Swedish  origin,  signifies  a  heavy  stone. 
Wolfram  is  a  frequent  and  troublesome  impurity 
among  tin-ores,  and  miners  regard  it  as  a  sign  of 
tin. 

Tungsten  itself  is  a  grayish  metal,  of  specific 
gravity  19.26,  being  almost  as  heavy  as  gold.  Its 
addition  to  steel  in  small  quantities  is  said  to  give 
the  latter  superior  hardness  and  fineness. 

Like  molybdenum,  tungsten  forms  very  compli- 
cated compounds.  Some  of  them  have  great  theo- 
retical interest,  but  need  no  description  here.  Tung- 
sten  trioxide  and  tungstic  acid,  WO3  and  H2WO4, 
show  its  relations  to  the  other  metals  of  the  group, 
and  the  hexchloride,  WC16,  indicates  its  sexivalency. 

*  The  experiment  is  a  good  and  easy  one  for  the  pupil  to  try. 


258  INORGANIC  CHEMISTRY. 

One  of  the  tungstates  of  sodium  is  sometimes  used 
as  a  mordant,  and  also  for  rendering  cloth  fabrics 
uninflammable. 

URANIUM,  atomic  weight  239,  is  another  of  the 
rarer  metals.  When  pure,  it  is  silver-white,  very 
difficultly  fusible,  and  of  specific  gravity  18.685.  It 
is  found  in  a  considerable  number  of  minerals,  but 
is  generally  obtained  from  pitchblende,  an  impure 
U3O8.  This  oxide  is  a  compound  of  two  others, 
UO2  and  UO3 ;  and  still  another,  UO4,  has  recently 
been  discovered.  The  trioxide,  UO3,  is  a  yellow 
powder ;  and  from  it  a  series  of  salts,  similar  in 
composition  to  the  pyrochromates,  are  derived. 
The  sodium  and  ammonium  uranates,  Am2U2O7  and 
Na2U2O7,  both  occur  in  commerce  under  the  name 
of  "uranium  yellow,"  and  are  used  in  coloring  glass 
and  porcelain.  The  uranium  glass  has  a  peculiar 
greenish-yellow  color  (canary  glass),  and  is  highly 
fluorescent.  In  two  other  series  of  salts  uranium  is 
basic.  The  uranic  nitrate  and  acetate  are  useful 
laboratory  reagents. 

Although  uranium  and  its  compounds  have  but 
limited  importance,  the  metal  itself  affords  a  good 
illustration  of  the  law  of  Dulong  and  Petit.  This  is 
a  physical  law  of  much  value  in  the  determination 
of  atomic  weights,  and  therefore  it  may  be  profita- 
bly considered  here. 

If  two  different  substances,  equal  in  weight,  be 
exposed  to  the  same  source  of  heat,  they  will  be 
found  to  gain  in  temperature  with  very  unequal 
rapidity.  A  kilogramme  of  water,  for  example,  re- 
quires about  thirty  times  as  much  heat  to  raise  its 
temperature  one  degree  as  is  required  to  produce 
the  same  effect  upon  the  same  quantity  of  mercury. 


THE  CHROMIUM  GROUP. 


259 


Hence  the  specific  heat  of  mercury  is  said  to  be  one 
thirtieth  of  that  of  water.  By  the  term  specific  heat 
we  express  the  relative  amounts  of  heat  needed  to 
raise  equal  weights  of  substances  through  equal 
ranges  of  temperature.  Water  has  the  highest 
specific  heat  of  any  substance  known,  and  is  taken 
as  the  standard  of  comparison  or  unity.  The  spe- 
cific heat  of  other  substances  is  expressed  in  frac- 
tions of  unity.  In  other  words,  the  quantity  of 
heat  necessary  to  raise  the  temperature  of  one  kilo- 
gramme of  water  i°  C.  is  said  to  be  one  unit.  The 
fraction  of  such  a  unit  which  is  required  to  raise  the 
temperature  of  a  kilogramme  of  any  other  substance 
i°  C.  is  called  its  specific  heat. 

Now,  the  law  of  Dulong  and  Petit  is  based  upon 
the  fact  that,  when  the  specific  heats  of  the  metals 
are  multiplied  by  their  atomic  weights,  the  products 
are  sensibly  equal.  The  product  in  each  case  is 
called  the  atomic  heat  of  the  metal ;  and  the  law 
which  is  deduced  is  as  follows :  all  the  element- 
ary atoms  have  equal  capacities  for  heat*  This  is 
shown  in  the  table,  which  includes  some  of  the 
non-metals : 

Table  of  Specific  and  Atomic  Heat. 


NAME. 

.83 

ff  M 

g 

id 

| 

i* 
g 

NAME. 

•3S 
|f 

iij 

£  $ 
$* 

is 

<-* 

Aluminum 
Antimony 
Arsenic  .  . 

27. 
120. 

75'. 

.2253 

•Q.-23 
.0822 

6.08 
6.28 

6.16 

Calcium  .... 
Cerium  
Cobalt  

40. 
141. 

CQ 

.1686 
.0448 
.1062 

6.74 
6.32 
626 

Barium  .  . 
Bismuth  . 
Cadmium 

137- 
208. 

112. 

.05 
.0305 
.0548 

6.85 
6.34 

6.14 

Copper  
Didymium  .  . 
Gallium  

63.3 
145- 
69. 

.0951 
.0456 
.079 

6.00 
6.6  1 

545 

*  For  fuller  discussions  of  this  law,  see  Wurtz's  "  Atomic  Theory, 
and  Chapter  III  of  Remsen's  "  Theoretical  Chemistry." 


26o  INORGANIC  CHEMISTRY. 

Table  of  Specific  and  Atomic  Heat  (continued'). 


NAME. 

ii 

<* 

HL- 

Z$ 
eg* 

.a  . 

I-S 

NAME. 

,a5 

efcJO 
3 

<* 

o 

1C     . 

HI 
eg* 

^ 

11 
<* 

Gold  

106.5 

.0316 

6.T8 

Platinum  .... 

*95- 

•0323 

6.29 

Indium 

Iia  C 

.0565 

6.61 

Rhodium  .... 

104.? 

.0580 

6.O3 

Iridium  

193. 
56. 

.0326 
.1116 

6.29 
6.25 

Ruthenium  .  . 
Selenium..  .  . 

104.? 

79- 

.0611 
.0860 

6-35 
6.79 

O^d.1 

6  87 

Silver         .  .  • 

108 

OCCQ 

6  04. 

178 

OJ.  l8 

6  18 

Sodium  .    ... 

27. 

2Q7A 

6  75 

Lead 

2O7. 

.03  Is; 

6.52 

Sulphur..    .  . 

32. 

.2026 

6/]8 

Lithium  

7. 

.0108 

6.59 

Tellurium  .  . 

125. 

•°475 

5-94 

Magnesium.. 
Manganese.. 

24. 

55- 
200 

.2499 
.1217 

O777 

6.00 
6.70 
666 

Thallium.    .  . 
Thorium  .    .  . 
Tin  

204. 
232. 
118. 

.0325 
.0279 

.0548 

6.63 
6.47 
6  17 

Molybdenum 
Nickel 

95. 

58. 

.0722 
.IO75 

6-93 
6.23 

Tungsten.   .  . 
Uranium  .  .  . 

184. 

239- 

.0334 

.0275 

6.15 
6.56 

TOO   ? 

O3II 

6  19 

Zinc  .        .... 

65. 

.OQ7Q 

6  OQ 

Palladium.  .  . 
Phosphorus  .  . 

106. 
Si- 

.0592 
.202 

6.27 
6.26 

Zirconium..  . 

90. 

.0667 

u.uy 

6.00 

There  are  a  few  apparent  exceptions  to  the  law,  but 
they  need  no  notice  here.  The  slight  variations 
from  exact  equality  in  the  column  of  atomic  heats 
are  due  to  unavoidable  errors  of  experiment. 

In  the  case  of  uranium  there  was  until  recently 
some  doubt  as  to  whether  its  atomic  weight  was 
239;  or  only  half  as  great ;  and  the  analyses  of  its 
compounds  gave  formulae  which  agreed  equally 
well  with  either  value.  Thus,  in  UO3  we  have  239 
parts  of  uranium,  combined  with  48  of  oxygen ; 
while,  if  U  =  119.5,  we  should  write  the  formula 
U2Os,  and  express  precisely  the  same  ratio.*  The 
uncertainty  was  at  last  dispelled  by  a  determination 
of  the  specific  heat  of  uranium,  which  Zimmermann 
found  to  be  .028.  This,  multiplied  by  239,  gives  a 

*  The  values  120  and  240  have  commonly  been  given  to  U,  but 
119.5  and  239  are  probably  more  nearly  exact. 


THE  CHROMIUM  GROUP.  261 

value  for  the  atomic  heat  of  6.69,  which  agrees  with 
the  other  metals;  whereas  119.5  would  have  given 
a  product  very  far  too  small.  In  many  other  cases 
the  atomic  weights  of  elements  have  been  unsettled 
until  the  specific  heats  could  be  ascertained,  and 
that  value  selected  which  agreed  best  with  Dulong 
and  Petit's  law. 


CHAPTER  XXIX. 

MANGANESE  AND   IRON. 

MANGANESE,  iron,  nickel,  and  cobalt  are  so 
closely  related  that  they  may  fairly  be  called  the 
iron  group  of  metals.  They  are  near  each  other  in 
metallic  properties,  and  their  compounds  have  very 
many  points  of  similarity.  In  valency  they  range 
from  two,  to  four,  six,  and  eight. 

MANGANESE  is  one  of  the  commoner  elements, 
and  is  very  widely  diffused.  It  occurs  in  many 
rocks  and  minerals,  but  its  chief  ores  are  pyrolusite, 
MnO2,  and  manganite,  Mn2O3,  H2O.  The  metal  it- 
self is  somewhat  difficult  to  prepare,  and  in  appear- 
ance is  similar  to  cast-iron.  It  oxidizes  very  easily, 
is  slightly  magnetic,  very  difficultly  fusible,  and  has 
a  specific  gravity  of  8.0.  Its  atomic  weight  is  55. 

With  oxygen,  manganese  combines  to  form  the 
oxides  MnO,  Mn2O3,  Mn3O4,  MnO2,  and  Mn2O7. 
From  the  monoxide,  MnO,  a  series  of  manganese 
salts  are  derived,  which  are  mostly  rose-colored. 
Manganous  sulphate,  MnSO4,  5H2O,  and  manganous 
chloride,  MnCl2, 4H2O,  are  the  salts  most  often  seen. 
In  solutions  of  manganese  compounds  ammonium 
sulphide  produces  a  flesh  -  colored  precipitate  of 
MnS.  From  Mn2O3,  which  is  also  a  basic  oxide,  the 
manganic  salts  are  prepared.  Manganic  sulphate, 


MANGANESE  AND  IRON.  263 

Mn2(SO4)3,  unites  with  the  alkaline  sulphates  to 
form  alums ;  and  in  this  particular  manganese  and 
chromium  may  be  classed  in  one  group  with  alu- 
minum and  iron.  Most  of  the  manganic  salts  are 
brown. 

The  oxides  MnO2  and  Mn3O4  are  neutral  oxides ; 
that  is,  they  form  neither  acids  nor  bases.  The  first 
of  these,  commonly  known  as  black  oxide  of  man- 
ganese, occurs  abundantly  in  many  localities,  and  is 
simply  ground  up  to  powder  and  sent  into  com- 
merce. Enormous  quantities  of  it  are  used  in  mak- 
ing chlorine  and  bleaching-powder,  in  the  prepara- 
tion of  oxygen,  and  as  a  material  from  which  all  the 
other  compounds  of  manganese  may  be  derived. 

Manganese  forms  two  acids :  manganic  acid, 
H2MnO4,  known  only  in  its  salts,  and  permanganic 
acid,  HMnO4,  which  is  derived  from  the  oxide  Mn2O7. 
Mn2O7-[-H2O=2HMnO4.  Manganic  acid  belongs  in 
the  same  class  with  sulphuric  and  chromic  acids; 
while  permanganic  acid  is  similar  in  structure  to 
perchloric  acid.  The  salts  KC1O4  and  KMnO4  are 
isomorphous.  The  manganates  are  green ;  the  per- 
manganates violet,  red,  or  purple. 

EXPERIMENT  94. — Mix  a  little  MnO2  with  so- 
dium carbonate,  and  fuse  the  mixture  in  the  outer 
blow-pipe  flame  upon  a  slip  of  platinum  foil.  A 
green  mass  of  sodium  manganate  will  be  formed, 
and  by  the  production  of  this  green  color  even  the 
smallest  traces  of  manganese  may  be  detected.  Dis- 
solve the  fused  mass  in  cold  water,  and  let  the  solu- 
tion stand  freely  exposed  to  the  air.  It  will  slowly 
change  color,  passing  from  green  through  a  series 
of  intermediate  tints,  until  at  last  it  becomes  a  su- 
perb purple.  These  changes,  which  end  in  the  pro- 


264  INORGANIC  CHEMISTRY. 

duction  of  sodium  permanganate,  caused  the  green 
mass  to  receive  the  popular  name  of  "  chameleon 
mineral." 

Potassium  permanganate,  KMnO4,  is  an  impor- 
tant disinfectant.  It  forms  nearly  black  crystals 
with  a  semi-metallic  reflection  from  their  surfaces, 
and  it  dissolves  easily  in  water  to  an  intense  purple 
fluid.  Even  a  trace  of  the  salt  will  impart  a  rosy 
color  to  a  large  amount  of  water,  and  concentrated 
solutions  of  it  are  opaque.  It  is  a  powerful  oxidiz- 
ing agent,  and  is  much  used  as  a  reagent  in  chemical 
analysis.  Putrid  water,  or  water  which  has  acquired 
an  unpleasant,  woody  taste,  from  long  keeping  in 
wooden  cisterns  or  casks,  may  be  rendered  sweet  by 
the  addition  of  a  very  little  potassium  permanganate. 

IRON,  atomic  weight  56,  is  the  most  familiar  and 
useful  of  all  metals,  and  one  of  the  most  abundant. 
It  is  contained  in  a  vast  number  of  minerals,  in 
practically  all  rocks  and  soils,  in  the  water  of  many 
springs,  in  plants,  and  in  the  red  coloring-matter  of 
blood.  Occasionally  it  is  found  free  in  nature,  and 
a  considerable  proportion  of  the  meteoric  masses 
which  fall  to  the  earth  consist  of  metallic  iron.  One 
such  mass  from  Brazil  weighed  32,000  pounds. 

But,  although  iron  is  so  widely  diffused,  it  is 
practically  manufactured  from  only  a  very  few  ores. 
These  are  essentially  the  magnetic  oxide,  Fe3O4; 
hematite,  Fe2O3 ;  limonite,  2Fe2O8,  sH2O  ;  and  cha- 
lybite  or  spathic  iron,  FeCO8.  Of  these,  the  mag- 
netic ore  is  the  richest,  containing,  when  pure,  72.5 
per  cent  of  iron. 

Pure  iron  is  rarely  seen.  It  is  silvery  white, 
softer  than  wrought-iron,  almost  infusible,  and  has 
a  specific  gravity  of  7.8  to  8.0.  It  is  extraordinarily 


MANGANESE  AND  IRON.  26$ 

malleable  and  ductile,  and  at  the  same  time  very 
tenacious ;  so  that,  even  in  the  finest  wire,  it  can 
support  a  considerable  weight.  The  symbol,  Fe,  is 
from  the  Latin  ferrum. 

All  commercial  iron  contains  carbon,  and  its 
properties  vary  remarkably  according  to  the  pro- 
portion of  the  latter.  Wrought-iron,  or  malleable 
iron,  contains  less  than  half  a  per  cent  of  this  im- 
purity ;  cast-iron  contains  from  two  to  six  per  cent, 
partly  or  wholly  in  chemical  combination ;  steel  is 
intermediate  between  the  other  two. 

Wrought-iron  is  tough  and  fibrous  in  structure, 
and  can  be  worked  at  a  red  heat  by  rolling  or  ham- 
mering. At  the  highest  available  temperatures  it 
does  not  fuse,  but  merely  becomes  pasty ;  but,  in 
this  condition,  two  masses  may  be  compactly  ham- 
mered or  welded  together.  This  capability  of  weld- 
ing is  one  of  its  most  valuable  properties.  It  is 
sometimes  prepared  directly  from  the  ore,  by  heat- 
ing the  latter  in  a  proper  furnace  with  charcoal,  and 
afterward  purifying  the  pasty  mass  from  adhering 
fuel  and  slag  by  thorough  hammering.  This  pro- 
cess, which  is  known  as  blooming,  has  been  in  use 
from  the  remotest  antiquity,  and  yields  a  remarka- 
bly fine  quality  of  metal.  It  is,  however,  too  ex- 
pensive to  be  largely  used  at  the  present  time ;  and 
to-day  malleable  iron  is  chiefly  prepared  by  burning 
out  the  carbon  from  cast-iron.  The  latter,  mixed 
with  a  certain  amount  of  ferric  oxide,  is  melted  on 
the  floor  of  a  reverberatory  furnace,  and  constantly 
stirred  or  shaken  until  it  becomes  pasty.  The 
spongy  lumps  are  then  taken  out,  and  worked  into 
shape  between  heavy  rollers.  The  whole  process  is 
technically  known  2&  puddling. 


266  INORGANIC  CHEMISTRY. 

Cast-iron,  which  is  a  comparatively  modern  prod- 
uct, is  made  in  the  blast-furnace  (Fig.  50).  This 
consists  of  a  tower  from  forty  to  ninety  feet  in 


FIG.  50. — Section  of  Blast  Furnace. 

height,  having  an  interior  diameter  of  from  four- 
teen to  seventeen  feet  in  the  maximum.  Internally 
it  is  like  two  hollow  cones  placed  base  to  base, 
and  it  is  lined  with  the  most  refractory  fire-brick. 
At  the  bottom,  air  is  blown  in  by  a  powerful  blast, 
through  pipes  which  are  called  tuyeres;*  and  ac- 

*  Pronounced  "  twyers." 


MANGANESE  AND  IRON.  26/ 

cordingly,  as  hot  or  cold  air  is  used,  we  have  hot 
and  cold  blast-furnaces  respectively.  The  hot-blast 
process  is  the  more  economical. 

The  furnace  is  fed  at  the  top,  and  alternate  lay- 
ers of  fuel,  ore,  and  limestone  are  put  in.  The  blast 
of  air  from  the  tuyeres  furnishes  oxygen,  vivid  com- 
bustion takes  place,  the  oxides  of  iron  are  reduced 
by  the  carbon,*  and  the  metal  is  set  free.  The  lat- 
ter dissolves  some  carbon,  fuses,  and  settles  to  the 
bottom  of  the  furnace,  where  it  is  drawn  off  from 
time  to  time  into  molds  made  of  sand.  The  object 
of  the  limestone  is  to  form  an  easily  fusible  slag 
with  the  silica  of  the  ore,  and  with  this  slag  many 
of  the  impurities  are  removed.  When  once  kin- 
dled, a  furnace  should  burn  continuously  for  months, 
or  even  years ;  were  the  semi-fluid  mass  to  solidify 
by  too  great  a  cooling,  it  would  have  to  be  dug  out 
at  great  expense  and  at  the  cost  of  serious  delay  to. 
the  iron-master. 

Cast-iron  or  pig-iron  occurs  in  several  forms,  but 
is  always  crystalline  in  structure  and  more  or  less 
brittle.  White  cast-iron  is  very  hard,  highly  crys- 
talline, and  quite  brilliant.  Gray  cast-iron  is  softer 
and  closer  grained.  Mottled  iron  is  intermediate 
between  the  other  two.  In  white  iron,  most  of  the 
carbon  is  combined  chemically  ;  in  gray  iron,  a  part 
has  separated  out  in  the  form  of  fine  .scales  of  graph- 
ite. Spiegeleisen  is  a  particularly  brilliant  white 
iron,  containing  about  six  per  cent  of  carbon  and 
some  manganese.  Common  impurities  in  iron  are 
silicon,  sulphur,  and  phosphorus.  The  last  two  ele- 

*  In  reality,  the  chemical  processes  which  take  place  in  the  blast- 
furnace are  quite  complicated.  In  them,  carbon  monoxide  plays  an 
important  part. 


268  INORGANIC  CHEMISTRY. 

ments  are  particularly  objectionable,  especially  if 
the  iron  is  to  be  either  puddled  or  made  into  steel. 
Sulphur,  in  wrought-iron,  renders  the  metal  brittle 
when  hot,  or  "hot-short";  the  presence  of  phos- 
phorus makes  it  brittle  when  cold,  or  "  cold-short." 

Steel  may  be  made  in  several  ways.  Carbon 
may  be  added  to  malleable  iron,  or  carbon  may  be 
withdrawn  from  cast-iron,  or  cast-iron  and  malle- 
able iron  may  be  melted  together  in  the  proportions 
needed  to  form  a  mixture  having  the  composition 
and  properties  of  steel.  The  last  method  is  adopted 
in  what  is  called  the  Siemens-Martin  process.  Of 
these  methods,  the  first  is  by  far  the  oldest.  Bars 
of  iron  are  packed  in  charcoal  in  tight  boxes  of  fire- 
clay, and  heated  red-hot  for  a  week  or  ten  days. 
Carbon  is  slowly  absorbed,  and  at  the  end  of  the 
operation  the  bars  are  found  to  have  a  curiously 
blistered  appearance.  By  melting  them  in  black- 
lead  crucibles  and  casting  them  in  ingots,  cast-steel 
is  obtained.  The  whole  process  is  known  as  the 
cementation  process,  and  cementation  steel  is  con- 
sidered the  best  for  fine  tools,  knives,  springs,  etc. 

The  second  process,  by  which  carbon  is  taken 
away  from  cast-iron,  was  invented  by  Bessemer  in 
1856.  In  this  process,  about  five  tons  of  melted  pig- 
iron  are  poured  into  an  egg-shaped  vessel  called  a 
"  converter  "  (Fig.  5 1),  through  which  a  powerful 
blast  of  air  can  be  blown.  The  converter  is  made 
of  the  strongest  wrought-iron,  and  lined  with  an  in- 
fusible layer  of  a  silicious  rock  resembling  fire-clay.* 
As  the  air  bubbles  through  the  molten  iron,  forced 
in  from  below,  the  temperature  rises,  carbon  is 

*  In  the  Gilchrist-Thomas  process,  which  removes  the  phosphorus 
from  the  iron,  the  converter  is  given  a  "  basic  lining  "  of  lime. 


MANGANESE  AND  IRON.  269 

burned  away,  and  the  metal  rapidly  approaches  the 
malleable  state.  Just  before  the  latter  is  reached, 
however,  a  quantity  of  melted  spiegel- 
eisen  is  added,  so  as  to  supply  just 
the  amount  of  carbon  needed  for  the 
production  of  good  steel.  The  latter 
is  then  poured  out  into  molds,  and  the 
operation  is  complete.  By  this  pro- 
cess iron  may  be  transformed  into 
steel  in  less  than  half  an  hour,  so  that 

f  ,.          .  .  .,,       FIG.    51. — Besse- 

the  saving  of  time  in  comparison  with     mer  converter. 
the  cementation  process  is  enormous. 
To-day,  in   consequence   of   Bessemer's  invention, 
steel  may  be  used  for  the  manufacture  of  rails,  car- 
axles,  bridge-girders,  boiler-plates,  and  cannon,  and 
for  a  multitude  of  other  purposes  to  which,  thirty 
years  ago,  it  was  too  expensive  to  be  applicable. 
It  is  no  exaggeration  to  say  that  the  Bessemer  pro- 
cess is  revolutionizing  the  iron  industry.* 

Steel  owes  its  value  to  a  variety  of  properties. 
Like  cast-iron  it  is  fusible,  like  wrought-iron  it  is 
malleable ;  it  is  capable  of  high  polish,  and  may  be 
rendered  exceedingly  hard.  If  heated  to  redness 
and  suddenly  quenched  in  cold  water,  it  becomes 
both  hard  and  brittle ;  but  upon  reheating  and  cool- 
ing slowly,  it  may  again  be  rendered  soft.  By  care- 
fully regulating  the  heatings  and  coolings,  interme- 
diate degrees  of  hardness,  brittleness,  and  elasticity 
may  be  attained  ;  and  by  this  process  of  "  temper- 
ing," steel  is  adapted  to  a  wide  diversity  of  uses. 

Like  manganese  and  chromium,  iron  forms  two 

*  The  best  large  treatise  on  the  metallurgy  of  iron  and  steel  is 
Percy's.  A  good  summary  of  the  subject  is  given  in  Roscoe  and  Schor- 
lemmer's  "  Treatise  on  Chemistry,"  vol.  ii,  part  ii,  pp.  34-83. 


2  70  INORGANIC  CHEMISTRY. 

distinct  series  of  compounds,  in  which  it  plays  the 
part  of  base.  It  also  forms  a  very  unstable  series  of 
salts,  corresponding  to  ferric  acid,  H2FeO4,  which 
are  analogous  to  the  chromates  and  manganates. 

The  ferrous  salts,  in  which  iron  is  apparently  biv- 
alent, are  similar  in  structure  to  the  salts  of  zinc, 
magnesium,  and  manganese.  They  may  be  regard- 
ed as  derived  from  ferrous  oxide,  FeO,  and  are 
mostly  pale  green  in  color.  By  adding  any  caustic 
alkali,  KOH,  NaOH,  or  AmOH,  to  a  solution  of  a 
ferrous  hydroxide,  Fe(OH)2,  is  obtained  as  a  green- 
ish precipitate.  Ferrous  chloride,  FeCl2, 4H2O,  is 
easily  prepared  by  dissolving  iron  in  hydrochloric 
acid,  and  is  used  in  some  processes  of  metallurgy. 
Ferrous  carbonate,  FeCO3,  is  a  crystalline  mineral, 
which,  in  a  crude  and  impure  state,  is  one  of  the 
most  important  ores  of  iron.  Ferrous  sulphide, 
FeS,  is  made  by  fusing  iron  and  sulphur  together 
in  the  proportion  indicated  by  their  atomic  weights, 
and  is  employed  in  the  laboratory  for  the  genera- 
tion of  sulphuretted  hydrogen.  But  the  most  im- 
portant of  the  ferrous  compounds  is  the  sulphate, 
FeSO4,  7H2O,  which  is  commonly  known  as  green 
vitriol  or  copperas.  It  is  prepared  by  dissolving 
iron  in  sulphuric  acid,  or  by  slowly  oxidizing  iron 
pyrites ;  and  forms  large,  pale-green  crystals  which 
behave  with  regard  to  their  water  of  crystallization 
precisely  like  the  sulphates  of  zinc  and  magnesium. 
With  tannin,  or  with  solution  of  galls,  ferrous  sul- 
phate strikes  a  deep-black  color,  on  which  account 
it  is  used  in  great  quantities  for  the  manufacture  of 
ink.  It  also  has  some  value  as  a  disinfectant,  acting 
as  an  absorbent  of  oxygen. 

All  ferrous  salts  tend  to  take  up  oxygen  from 


MANGANESE  AND  IRON.  2Jl 

the  air,  and  to  become  converted  into  ferric  com- 
pounds, which  are  mostly  red  or  yellow.  Ferric 
oxide,  Fe2O3,  is  the  important  ore,  hematite  ;  and 
also,  artificially  prepared,  is  used  both  as  a  material 
for  polishing  glass  and  precious  metals,  and  as  a 
pigment  under  the  name  of  Venetian-red.  Jeweler's 
rouge  and  crocus-powder  are  merely  ferric  oxide. 
Several  ferric  hydroxides  are  found  as  mineral  spe- 
cies, and  are  valuable  ores.  An  artificial  hydroxide, 
Fe2  (OH)6,  is  produced  by  caustic  alkalies  in  solu- 
tions of  ferric  salts,  as  a  reddish-brown  precipitate. 
It  is  used  in  some  processes  for  purifying  coal-gas, 
and  as  an  antidote  for  arsenical  poisoning.  Iron- 
rust  is  another  ferric  hydroxide,  produced  by  the 
joint  action  of  air  and  water  upon  metallic  iron. 
Ferric  chloride,  Fe2Cl6,  and  ferric  sulphate,  Fe2(SO4)3, 
are  both  important  ferric  salts.  The  chloride  is  used 
as  a  reagent  in  the  laboratory,  and  also  in  medicine 
as  a  material  to  stop  bleeding.  The  sulphate  unites 
with  alkaline  sulphates  to  form  alums,  which  cor- 
respond perfectly  to  the  similar  salts  of  aluminum 
and  chromium. 

The  magnetic  oxide,  Fe3O4,  is  a  very  important 
ore,  and  is  also  met  with  as  iron-scale  in  the  black- 
smith-shops. By  heating  iron  in  dry  steam  it  may 
be  coated  with  a  thin  black  film  of  this  oxide  and 
protected  against  rust.  Fe3O4  is  a  neutral  oxide,  and 
may  be  regarded  as  FeO  -\-  Fe2O3.  Iron  pyrites, 
FeS2,  is  a  common  mineral,  which  is  sometimes 
called  "  fools'  gold."  It  is  yellow  and  metallic  in 
appearance,  but,  unlike  gold,  it  may  be  pulverized 
under  a  hammer.  It  is  used  as  a  source  of  copperas, 
and  also  in  the  manufacture  of  sulphuric  acid. 

EXPERIMENT  95. — Dissolve  some  iron  filings  in 


272  INORGANIC  CHEMISTRY 

dilute  sulphuric  acid,  and  divide  the  solution  into 
two  parts.  Add  ammonia  to  one  portion,  and  note 
the  color  of  the  ferrous  hydroxide  which  is  thrown 
down.  Boil  the  other  portion  with  a  few  drops  of 
strong  nitric  acid,  and  observe  the  change  of  tint. 
Again  precipitate  with  ammonia,  and  note  the  pe- 
culiarities of  the  ferric  hydroxide  which  will  be  ob- 
tained. Nitric  acid  oxidizes  ferrous  compounds  to 
the  ferric  state. 


CHAPTER  XXX. 

NICKEL,  COBALT,  AND  COPPER. 

NICKEL  and  cobalt  are  comparatively  rare  met- 
als, having  a  decided  resemblance  to  iron.  Both 
are  white  and  malleable,  but  cobalt  has  a  very  slight 
reddish  tinge.  Both  are  strongly  magnetic,  and 
their  specific  gravity  is  not  far  from  9.  The  atomic 
weight  of  nickel  is  58 ;  that  of  cobalt  is  59. 

The  chief  supply  of  nickel  comes  from  Ger- 
many, Pennsylvania,  and  New  Caledonia,  and  quite 
recently  valuable  deposits  of  a  nickel-ore  have  been 
found  in  Oregon.  The  ores  are  mostly  sulphides, 
arsenides,  and  silicates  of  nickel,  and  the  extraction 
of  the  metal  is  a  somewhat  complicated  matter.  It 
is  used  as  an  ingredient  of  small  coins  by  several 
nations,  and  German  silver  is  an  alloy  of  copper, 
zinc,  and  nickel.  Of  late  years  the  process  of  elec- 
troplating with  nickel  has  assumed  considerable  im- 
portance. The  metal  forms  a  beautiful  white  sur- 
face which  does  not  rust,  and  is  chiefly  applied  to 
articles  of  copper,  brass,  or  steel. 

The  compounds  of  cobalt  and  nickel  resemble 
those  of  iron,  except  that  their  lower  salts  do  not 
so  readily  oxidize  to  form  the  higher.  The  oxides 
CoO,  NiO,  Co2O3,  Ni2O3,  yield  series  of  derivatives 
similar  to  the  ferrous  and  ferric  compounds.  The 


274  INORGANIC  CHEMISTRY. 

nickelous  salts  are  generally  green,  and  the  sulphate, 
NiSO4,  ;H2O,  the  chloride,  NiCl2,  6H2O,  and  the  ni- 
trate, Ni(NO3)2,  6H2O  are  the  most  important.  The 
salt  employed  in  nickel-plating  is  the  double  sul- 
phate NiSO4,  Am2SO4,  6H2O. 

The  cobaltous  salts  are  remarkable  in  regard 
to  their  colors.  They  are  rose-red  when  hydrat- 
ed,  blue  when  anhydrous.  Heat  cobalt  sulphate, 
CoSO4,  7H2O,  until  its  water  of  crystallization  is  ex- 
pelled, and  its  red  color  will  pass  into  the  blue  tint 
of  CoSO4. 

EXPERIMENT  96. — Dissolve  cobalt  chloride  in 
water,  and  with  a  small  brush  apply  the  solution  to 
a  sheet  of  white  paper.  When  the  latter  is  dry, 
scarcely  any  color  can  be  perceived  upon  it,  but  by 
gently  heating  before  a  fire  it  will  become  distinctly 
blue.  The  solution,  therefore,  may  be  used  as  a 
"  sympathetic  ink  "  ;  and  a  letter  written  with  it  will 
be  legible  only  when  the  paper  is  warm. 

Some  of  the  cobalt  compounds  are  valuable  col- 
ors, especially  for  glass  and  porcelain.  Smalt  blue 
is  a  silicate  of  cobalt,  which  withstands  the  highest 
temperatures  of  the  porcelain  oven.  Thenard's  blue 
contains  the  oxides  of  cobalt  and  aluminum.  Rin- 
mann's  green  consists  of  the  oxides  of  cobalt  and  zinc. 

EXPERIMENT  97. — Place  a  crystal  of  alum  on  a 
charcoal  support,  and  heat  it  before  the  blow-pipe. 
Moisten  the  infusible  residue  with  a  drop  of  cobalt 
nitrate  solution,  and  heat  again.  The  mass  will  be- 
come blue.  Repeat  the  experiment,  using  zinc  ox- 
ide instead  of  alum,  and  a  green  will  be  produced. 
Magnesia,  treated  in  the  same  way  with  cobalt  ni- 
trate, gives  a  pale  rose.  By  cobalt  compounds  a 
borax  bead  is  colored  intensely  blue. 


NICKEL,    COBALT,    AND  COPPER.  275 

COPPER,  atomic  weight  63.3,  is  a  metal  having 
some  relationship  to  the  iron  group  on  one  side, 
and  closely  allied  to  silver  and  mercury  on  the 
other.  Like  mercury,  it  forms  two  sets  of  com- 
pounds, a  cuprous  and  a  cupric  series,  but  some  of 
its  salts  are  quite  analogous  to  similar  compounds 
of  iron.  The  symbol,  Cu,  is  from  the  Latin  cu- 
prum. 

Copper  is  widely  diffused  in  the  mineral  king- 
dom, both  as  native  metal  and  in  a  great  variety 
of  compounds.  Native  copper  is  abundant  in  the 
Lake  Superior  mining  region,  and  a  single  mass 
weighing  four  hundred  and  twenty  tons  was  once 
found.  Important  ores  of  copper  are  cuprous  sul- 
phide, Cu2S  ;  the  oxides,  Cu2O  and  CuO  ;  bornite, 
Cu3FeS3;  copper  pyrites,  CuFeS2;  and  malachite, 
CuCO3,  Cu(OH)2.  The  last-named  mineral  is  often 
used  as  an  ornamental  green  stone. 

The  process  of  extracting  copper  from  its  ores 
is  generally  somewhat  complicated.  The  native 
metal,  of  course,  only  needs  to  be  put  through  a 
refining  operation  in  order  to  be  prepared  for 
market ;  and  the  oxides  and  carbonates  of  copper 
may  be  easily  reduced  by  heating  with  carbon ;  but 
in  most  smelting-works  the  metallurgist  has  to  deal 
with  sulphides  containing  iron.  These  are  com- 
monly treated  as  follows:  The  ore  is  first  roasted 
in  a  reverberatory  furnace,  whereby  the  cuprous 
sulphide  is  partly  converted  into  oxide.  It  is  then 
mixed  with  sand,  or  with  a  fusible  silicate,  and 
melted ;  the  copper  regains  sulphur,  while  the  iron 
is  oxidized,  and  runs  off  as  a  part  of  the  slag.  The 
cuprous  sulphide,  or  "  coarse  metal,"  thus  obtained 
is  re-roasted  and  re-melted,  and  so  on,  until  all  the 


2/6  INORGANIC  CHEMISTRY. 

iron  contained  in  the  ore  has  been  slagged  off,  and 
only  a  pure  cuprous  sulphide,  or  "  fine  metal,"  re- 
mains. The  latter  is  then  partly  oxidized  by  roast- 
ing, and  the  mixture  of  oxide  and  sulphide  is  finally 
fused ;  sulphur  dioxide  is  driven  off,  and  metallic 
copper  is  left  behind. 

2CuO  +  Cu2S  =  4Cu  +  SO2. 

In  the  Hunt  and  Douglas  process  the  sulphides 
of  copper  are  roasted,  and  then  treated,  in  pow- 
der, with  a  solution  of  ferrous  chloride.  Copper 
goes  into  solution,  and  is  afterward  precipitated 
in  the  metallic  state  by  the  addition  of  scrap-iron. 
The  latter  reproduces  ferrous  chloride,  which 
may  be  applied  to  another  charge  of  ore,  etc. 
This  process  is  an  interesting  example  of  a 
class  of  metallurgical  processes  which  are  fast 
assuming  industrial  importance.  The  precipita- 
tion of  copper  by  iron  may  be  illustrated  as  fol- 
lows : 

EXPERIMENT  98. — Dip  a  piece  of  bright  iron  or 
steel  into  a  solution  of  any  salt  of  copper.  Copper 
will  immediately  be  deposited  in  a  thin,  red  coating 
upon  the  surface  of  the  other  metal. 

Copper  is  interesting  on  account  of  its  being  the 
only  red  metal.  It  is  very  malleable  and  ductile, 
and  exceedingly  tenacious;  and,  after  silver,  it  is 
the  best  conductor  for  heat  and  electricity.  Bat- 
tery-wires and  lightning-conductors  are  usually 
made  of  it.  Its  specific  gravity  is  8.945,  and  it 
melts  at  about  1,050°  C.  At  very  high  temperatures 
it  is  slightly  volatile  ;  and  its  vapor,  either  free  or 
in  compounds,  colors  flame  green.  The  best  solv- 
ent for  copper  is  nitric  acid ;  boiling  sulphuric  acid 


NICKEL,   COBALT,  AND  COPPER.  277 

dissolves  it  also ;  but  hydrochloric  acid  attacks  it 
only  with  difficulty. 

Copper  is  not  only  useful  by  itself,  but  also  in 
many  alloys.  Brass,  bronze,  German-silver,  alumi- 
num bronze,  etc.,  have  been  already  described.* 
Copper  is  very  easily  deposited  by  electrolysis,  and 
this  fact  is  applied  in  the  process  of  electrotyping, 
as  follows :  A  page  of  type,  set  up  in  the  usual  way, 
is  first  copied  in  wax  or  plaster.  The  mold  thus 
obtained,  which  is  a  perfect  impression  of  the  type, 
is  then  dusted  over  with  powdered  graphite,  in 
order  to  render  it  a  conductor  of  electricity,  and 
suspended  in  a  solution  of  copper  sulphate.  It  is 
connected  by  a  copper  wire  with  the  zinc-pole  of 
the  battery,  while  the  other  pole  terminates  in  a 
copper  bar  or  plate,  which  is  also  immersed  in  the 
liquid.  As  the  current  passes,  copper  is  deposited 
upon  the  mold  in  a  coherent  film  of  any  desired 
thickness,  and  a  perfect  copy  of  the  type  is  obtained. 
By  this  process  copper  may  be  deposited  to  any 
extent ;  and  even  colossal  statues  may  be  electrically 
copied  by  precipitating  the  metal  gradually  upon 
their  plaster  casts.  In  electro-metallurgy  copper 
has  many  applications.f 

The  cuprous  compounds  have  little  importance, 
except  that  cuprous  oxide,  Cu2O,  is  used  for  giving 
a  ruby-red  color  to  glass.  Most  of  the  cupric  salts 
are  green  or  blue  when  crystallized,  but  cupric 
sulphate,  CuSO4,  5H2O,  is  white  when  anhydrous. 
This  salt,  which  forms  large  blue  crystals,  may  be 
transformed  into  a  white  powder  by  careful  heat- 
ing. It  is  the  most  important  of  the  copper  com- 

*  See  under  zinc,  tin,  nickel,  and  aluminum. 

t  See  Gore's  work  on  electro-metallurgy,  previously  cited. 


2;8  INORGANIC  CHEMISTRY. 

pounds,  and  is  commonly  known  as  blue  vitriol.  It 
is  used  in  great  quantities  in  galvanic  batteries  for 
telegraph  lines,  in  electro  -  metallurgy,  in  calico- 
printing,  in  the  manufacture  of  Paris  green,  etc. 

Cupric  oxide,  CuO,  is  black ;  but  the  hydroxide, 
Cu(OH)2,  is  light  blue.  The  relations  between  them 
may  be  easily  illustrated  by  experiment. 

EXPERIMENT  99. — Dissolve  cupric  sulphate  in 
water,  and  add  a  little  caustic  soda  to  the  cold  solu- 
tion. A  blue  precipitate  of  Cu(OH)2  will  fall,  which 
will  be  transformed  into  black  CuO,  upon  boiling. 

CuSO4  +  2NaOH  =  Na2SO4  +  Cu(OH)2. 
Cu(OH)2  =  CuO  +  H2O. 

Repeat  the  experiment,  using  ammonia- water  in- 
stead of  caustic  soda.  The  precipitate  at  first 
formed  will  redissolve  in  an  excess  of  the  precipi- 
tant, yielding  an  intensely  deep-blue  solution.  This 
reaction  furnishes  a  most  delicate  test  for  copper. 

In  this  experiment  with  ammonia  a  peculiar 
compound  is  formed  having  the  formula  CuSO4, 
2NH3.  With  other  copper  salts  other  similar  com- 
pounds will  be  produced ;  all  of  which  may  be  re- 
garded as  salts  of  a  peculiar  complex  base,  called 

XNH 

cuprammonium,  Cu  j^p^8,  derived  from  two  am- 
monium atoms  by  the  replacement  of  two  hydro- 
gen atoms  by  one  atom  of  dyad  copper.  Many 
such  complex  bases  are  known,  and  they  have  great 
theoretical  interest. 

All  the  copper  compounds  are  very  poisonous. 
Hence  cooking  utensils  of  copper,  such  as  preserv- 
ing-kettles and  the  like,  should  be  used  only  with 
extreme  care.  They  should  always  be  kept  clean 


NICKEL,   COBALT,  AND  COPPER. 


279 


and  bright,  and  acid  fruits  or  preserves  should  not 
be  left  long-  in  contact  with  them.  This  statement 
applies  also  to  brass.  The  dangerous  pigments  con- 
taining arsenic  and  copper  were  described  in  a  pre- 
vious chapter. 


CHAPTER  XXXI. 

GOLD,   AND   THE   PLATINUM   GROUP. 

GOLD,  atomic  weight  196.5,  is  almost  invariably 
found  in  the  uncombined  state.  The  only  exception 
is  in  the  case  of  certain  tellurides,  which  generally 
contain  both  gold  and  silver.  To  some  extent,  gold 
in  dust,  grains,  or  nuggets,  is  washed  out  from  loose 
soil  and  gravel,  or  found  imbedded  in  rock;  but 
the  larger  yield  is  from  invisible  particles  diffused 
through  veins  of  iron  pyrites  or  quartz.  The  gold- 
bearing  rock  is  crushed  to  powder,  and,  if  it  contains 
much  pyrites,  is  roasted ;  the  mass  is  then  agitated 
with  mercury,  which  readily  amalgamates  with  the 
more  precious  metal.  The  mercury  is  finally  dis- 
tilled off  and  recovered  for  use  in  future  operations, 
while  metallic  gold  remains  behind. 

Gold,  thus  obtained,  is  rarely  pure.  It  gener- 
ally contains  some  silver ;  and  copper,  iron,  arsenic, 
and  other  metals  are  common  impurities.  When 
base  metals  are  present,  it  is  easily  refined  by  forc- 
ing chlorine  gas  through  it  while  in  the  melted 
state ;  the  impurities  form  chlorides,  which  either 
volatilize  or  float  in  an  easily  removable  scum,  and 
absolutely  pure  gold  remains  below.  From  silver 
it  is  generally  freed  by  a  process  known  as  quarta- 
tion.  The  crude  bullion  is  melted  with  an  additional 


GOLD,  AND    THE  PLATINUM  GROUP.      281 

quantity  of  silver,  so  that  it  shall  consist  of  three 
parts  of  the  latter  metal  to  one  of  gold ;  the  alloy  is 
then  rolled  into  thin  ribbons  and  treated  with  nitric 
acid  ;  the  silver  is  dissolved  out  as  nitrate,  and  pure 
gold  is  obtained. 

Gold  is  bright  yellow  in  color,  softer  than  silver, 
and  malleable  and  ductile  to  an  extraordinary  de- 
gree. One  grain  of  gold  can  be  made  to  gild  two 
miles  of  fine  silver  wire,  or  drawn  into  gold  wire  an 
eighth  of  a  mile  long.  It  may  be  beaten  into  leaves 
so  thin  that  280,000  would  only  make  the  thickness 
of  one  inch.  These  thin  leaves  transmit  light,  and, 
held  between  the  eye  and  the  sun,  appear  of  a 
greenish  color.  To  glass,  finely  divided  gold  im- 
parts a  fine  ruby-red  tint.  The  specific  gravity  of 
gold  is  19.3,  and  it  melts  at  about  i ,  100°  C.  For  prac- 
tical uses  pure  gold  is  too  soft ;  hence  it  is  always 
alloyed  with  copper  or  silver.  The  former  alloy 
renders  it  ruddier,  the  latter  makes  it  paler  in  color. 
The  coin  standard  of  the  United  States,  for  gold  as 
well  as  for  silver,  is  900  fine — that  is,  900  parts  of 
gold  to  100  of  alloy.  Jeweler's  gold  is  generally 
less  fine,  and  its  character  is  indicated  by  a  stand- 
ard called  the  carat.  Pure  gold  is  said  to  be  24 
carats  fine ;  three  fourths  pure  would  therefore 
be  1 8  carats;  two  thirds  fine  would  be  16  carats, 
etc.  With  mercury  gold  amalgamates  very  readily  ; 
hence  gold  rings  should  never  be  worn  when  quick- 
silver is  being  handled. 

EXPERIMENT  160. — Put  a  drop  of  mercury  upon 
a  bit  of  gold-leaf.  The  latter  will  dissolve,  forming 
a  white  amalgam. 

Gold  is  insoluble  in  all  acids,  except  the  mixture 
known  as  aqua  rcgia.  It  is  trivalent,  and  forms  two 


282  INORGANIC  CHEMISTRY. 

sets  of  compounds,  of  which  the  oxides  Au2O  and 
Au2O3,  and  the  chlorides  AuCl  and  AuCl3  are  good 
examples.  The  symbol  Au  is  from  the  Latin  aurum. 
The  aurous  compounds  are  of  slight  importance 
only. 

The  trichloride,  AuCl8,  is  the  most  useful  of  the 
gold  salts.  It  is  formed  whenever  gold  is  dissolved 
in  aqua  regia,  and  may  be  obtained  in  orange-yellow 
deliquescent  crystals  which  are  sensitive  to  light. 
It  is  used  in  "  toning  "  photographs,  and  in  electro- 
plating. As  applied  to  gold  the  latter  process  is 
almost  exactly  like  the  one  described  under  silver ; 
only  a  solution  of  the  double  cyanide  of  gold  and 
potassium  is  used,  with  a  gold  anode. 

PLATINUM,  atomic  weight  195,  is  always  more 
or  less  associated  with  five  other  metals,  iridium, 
osmium,  palladium,  rhodium,  and  ruthenium.  All 
these  metals  are  quadrivalent,  and  together  they 
are  known  as  the  platinum  group.  With  one  very 
rare  exception  *  they  are  found  in  the  free  state,  or 
rather  alloyed  with  one  another,  and  occasionally 
with  gold. 

Platinum  was  originally  brought  from  the  gold- 
washings  of  South  America  about  the  middle  of  the 
last  century.  Its  name,  from  platina,  is  the  Span- 
ish diminutive  of  plata,  silver,  and  hence  it  means 
"  little  silver."  The  greater  part  of  the  world's  sup- 
ply now  comes  from  the  Ural  Mountains.  The  ore 
occurs  in  grains  and  small  lumps,  mixed  with  vari- 
ous impurities,  from  which  it  has  to  be  separated  by 
a  complicated  process  of  refining.  It  is  a  steel-white 
metal,  fusible  only  at  or  above  the  temperature  of 
the  oxy hydrogen-flame,  and  of  specific  gravity  21.5. 

*  The  mineral  laurite,  ruthenium  sulphide,  found  in  Borneo. 


GOLD,   AND    THE  PLATINUM  GROUP.       283 

Of  all  the  other  metals,  iridium  and  osmium  only  are 
heavier,  and  that  but  a  trifle  ;  the  specific  gravity  of 
osmium,  which  is  heaviest  of  all,  is  22.5. 

Platinum  is,  like  gold,  insoluble  in  all  acids  ex- 
cept aqua  regia.  This  property,  together  with  its 
infusibility,  renders  it  extremely  useful  for  the  con- 
struction of  some  pieces  of  chemical  apparatus — 
such  as  dishes,  crucibles,  blow-pipe  tips,  foils,  wire, 
etc.  The  stills  used  for  concentrating  sulphuric 
acid  are  made  of  platinum,  and  the  metal  is  also 
employed  as  the  negative  element  in  Grove's  gal- 
vanic battery.  Without  platinum  utensils  the  chem- 
ical analysis  of  many  minerals  would  be  practi- 
cally impossible.  Commercial  platinum  is  generally 
stiffened  and  hardened  by  the  addition  of  a  little 
iridium.  Platinum-black  is  a  very  finely  divided 
platinum,  which  possesses  a  remarkable  power  of 
condensing  gases  within  its  pores.  One  volume  of 
this  substance  can  absorb  800  volumes  of  oxygen ; 
and  hence  it  serves  for  some  purposes  as  a  powerful 
oxidizing  agent. 

The  compounds  of  platinum  are  many,  compli- 
cated, and  theoretically  interesting.  There  is  a  pla- 
tinous  series,  corresponding  to  PtCl2  and  PtO  ;  and 
a  platinic  series,  represented  by  PtCl4  and  PtO2. 
Platinic  chloride,  which  is  prepared  by  dissolving 
platinum  in  aqua  regia  and  evaporating  to  dry- 
ness,  is  the  most  important  of  these  compounds. 
It  is  used  in  chemical  analysis  for  the  detection 
of  potassium  and  ammonium,  and  their  separa- 
tion from  other  bases.  Potassium  chloroplatinate, 
K2PtCl6  or  2KC1  +  PtCl4,  is  a  yellow  precipitate 
often  produced  in  the  laboratory. 

The  other  metals  of  the  group  are  rare  and  of 


284  INORGANIC  CHEMISTRY. 

little  relative  importance.  An  alloy  of  iridium  and 
osmium,  called  iridosmine,  is  often  found  in  gold- 
washings,  and  forms  brilliant  grains  which  are  hard- 
er than  steel,  and  are  used  for  tipping  gold  pens. 
A  process  has  recently  been  devised  for  fusing  them 
with  phosphorus,  and  so  obtaining  a  very  hard  and 
refractory  metal  which  may  be  used  for  a  variety  of 
practical  purposes.  Iridium-plating  has  very  lately 
been  patented,  and  may  soon  become  a  useful  in- 
dustry. 

Platinum,  iridium,  and  osmium  are  near  each 
other  in  atomic  weight  and  specific  gravity.  Pal- 
ladium, rhodium,  and  ruthenium  form  another  trio, 
having  atomic  weights  from  103  to  106,  and  specific 
gravities  from  1 1  to  12.  Palladium  is  a  silver-white, 
easily  workable  metal,  which  has  been  used  to  a 
limited  extent  in  philosophical  apparatus.  It  has 
the  property  of  absorbing  hydrogen,  and  forming 
what  is  apparently  an  alloy  with  the  latter.  This 
occluded  hydrogen  is  commonly  regarded  as  metal- 
lic, and  is  sometimes  called  hydrogenium. 


PART     II. 

ORGANIC  CHEMISTRY. 


CHAPTER  XXXII. 

PRELIMINARY   OUTLINE. 

IN  the  early  days  of  chemistry  a  sharp  distinc- 
tion was  drawn  between  the  compounds  derived 
from  plants  and  animals  and  those  obtained  from 
the  inorganic  or  mineral  kingdom.  Such  substances 
as  sugar,  starch,  the  fruit  acids,  and  albumen,  to- 
gether with  many  other  bodies  directly  derived 
from  them,  were  termed  organic  ;  while  the  min- 
erals, metals,  elements,  and  the  commoner  salts, 
all  of  non-living  origin,  were  classed  as  inorganic. 
These  classes  of  substances  were  regarded  as  per- 
fectly distinct ;  for  it  was  thought  that  in  the  pro- 
duction of  organic  bodies  some  peculiar  vital  force 
was  involved,  and  that  no  artificial  means  could 
ever  be  discovered  for  their  preparation.  In  1828, 
however,  Woehler  effected  the  synthesis  of  a  well- 
known  organic  compound,  urea,  from  wholly  inor- 
ganic materials ;  and  since  then  a  vast  number  of 
similar  syntheses  have  been  successfully  accom- 
plished. One  of  the  latest  triumphs  of  synthetic 
chemistry  has  been  the  artificial  preparation  of  in- 
digo. The  old  boundary  between  the  organic  and 


286  ORGANIC  CHEMISTRY. 

the  inorganic  has  been  thoroughly  broken  down, 
and  to-day  the  division  is  merely  one  of  conven- 
ience. 

Organic  compounds,  so  called,  are  remarkable 
for  their  great  number  and  complexity.  They  all 
agree  in  containing  carbon,  generally  in  union  with 
hydrogen,  oxygen,  nitrogen,  or  all  three.  Occa- 
sionally they  contain  sulphur  and  phosphorus  also ; 
and  many  of  the  artificial  products  contain  chlorine, 
bromine,  iodine,  boron,  silicon,  arsenic,  or  metals. 
All  of  them,  however,  owe  their  chief  characteris- 
tics to  carbon ;  and  on  this  account  organic  chem- 
istry is  now  commonly  defined  as  the  chemistry 
of  the  carbon  compounds.  Carbon,  by  virtue  of 
its  quadrivalence,  is  capable  of  building  up  com- 
plicated molecular  structures ;  and  in  doing  so  it 
seems  to  combine  with  itself  to  form  chains  or 
rings  of  carbon-atoms,  that  serve  as  centers  around 
which,  in  accordance  with  the  laws  of  valency, 
other  elements  can  be  grouped.  This  property  of 
carbon  will  become  evident  as  we  study  its  com- 
pounds. 

In  general,  organic  substances  may  be  most  con- 
veniently regarded  as  derived  from  compound  radi- 
cles, which,  in  most  cases,  are  hydrocarbons  having 
unsatisfied  bonds  of  valency.  Cyanogen,  however, 
and  carbon  monoxide,  being  unsaturated  compounds, 
play  an  important  part  in  organic  chemistry ;  and  so 
also,  but  in  a  different  way,  do  ammonia  and  ammo- 
nium. From  the  last  two  substances,  and  from  the 
compound  NO2,  many  of  the  more  important  nitro- 
genous bodies  are  derived. 

Although  hundreds  of  hydrocarbons  are  known, 
and  an  almost  infinite  number  are  theoretically  pos- 


PRELIMINARY  OUTLINE.  287 

sible,  they  may  all  be  easily  arranged  in  a  small 
number  of  comparatively  simple  series.  Methane, 
for  example,  CH4,  is  the  compound  of  carbon  and 
hydrogen  containing  the  highest  proportion  of  the 
latter  element ;  and  in  it  the  four  bonds  of  the  one 
are  exactly  satisfied  by  the  corresponding  number 
of  the  other.  This  compound  is,  however,  the  first 
member  of  a  series ;  the  higher  terms  being  C2H6, 
C3H8,  C4H10,  CgHtf,  and  so  on  up  to  C^H^.  Here 
each  hydrocarbon  differs  from  the  one  which  pre- 
cedes it  by  one  atom  of  carbon  and  two  of  hydrogen  ; 
the  second  being  the  first  plus  CH2,  and  so  on  as  far 
as  the  series  extends.  Such  a  series  is  known  as  an 
homologous  series ;  and  it  may  be  represented  by  one 
general  formula  CnH^  +  2.  All  other  hydrocarbons 
fall  into  similar  series,  and  for  each  series  a  similar 
formula  may  be  assigned,  as  is  shown  in  the  follow- 
ing scheme : 

Series  i.     CnH2n+2.      Lowest  member  known,  CH4.     • 

"        2.      CnHan.  "  "  "  C2H4. 

"       3.      CnHan-2.  "  "  "  C2H2. 

4.      CnHan-4.  "  "  CeHo. 

"     5-     CnH2n-6.  "  "  "        C6H6. 

"  6.  CnHan-8.  "  "  "  C8H8. 

"  7.  CnHan-io.  "  "  "  C8H8. 

"  8.  CnHan-12.  "  "  "  CIOH8. 

"  9-  CnHan-i4.  "  "  "  C12H10. 

"  10.  CnHan-i6.  "  "  "  C14H12. 

"  II.  CnHan-is.  "  "  «  C14H10. 

«        T -•>  /~"       TJ  tl  f        If 

12.  v^n  rlan— ao-  Ci7rli4. 

"        T  «?  f~*       T-T  «/^TT 

13.  ^n  ilan— 22.  dcliio. 

"        T  4  C*       T-I  «  /"•        TT 

14.  L,nrl2n-24.  CisHia. 
"     15.  CnHan- 26.  "                 "  "  CaoHu. 

"     1 6.  CnH2n-a8.  "                 "  "  

"     17.  CnH2n_30.  "  '      "  C22H14. 

l8.      CnHan-sa.  "  "  "  C2eHao. 


288  ORGANIC  CHEMISTRY. 

All  possible  hydrocarbons  are  covered  by  this 
system  of  formulas,  although  structural  formulas  of 
a  more  definite  kind  are  needed  to  bring  out  the 
relations  of  these  compounds  fully.  For  one  series 
no  representative  has  as  yet  been  discovered,  and 
in  several  series  the  lowest  possible  members  are 
not  known ;  but  some  of  these  gaps  will,  doubtless, 
be  filled  in  due  time. 

From  many  of  these  hydrocarbons  other  com- 
pounds are  derived  by  a  process  known  as  substitu- 
tion, in  which  atoms  of  hydrogen  are  successively 
replaced  by  atoms  of  other  univalent  elements  like 
chlorine,  bromine,  or  iodine.  Thus,  from  methane, 
CH4,  we  get  substitution  series  as  follows  : 

1.  CH4.  CH3C1.  CH2C12.  CHC1S.  CCI4. 

2.  CH4.  CH3Br.  CHaBra.  CHBr3.  CBr4. 

3.  CH4.  CHJ.  CHaI2.  CHI,.  CI4. 

For  benzene,  C6H6,  the  chlorine  substitution  series 
is  even  more  striking  ;  thus : 

C6H6.     C.H.C1.    C6H4C12.     C.H.C1,.    C6H2C14.    C6HC15.    C6C16. 

In  many  cases  compound  radicles  serve  as  agents 
of  substitution,  as  in  the  case  of  the  univalent  group 
NO2,  which  enters  into  numerous  important  sub- 
•stances.     A  few  examples  will  suffice  : 

C6H8.  C6H5(NO2).  C6H4(NO2)2. 

Benzene.  Nitrobenzene.  Dinitrobenzene. 

C3H803.  C3H5(N02)30s.  Etc. 

Glycerin.  Trinitroglycerin. 

Still  another  class  of  substitution  compounds  of 
the  highest  importance  is  derived  from  ammonia, 
NH3,  by  replacing  hydrogen  with  such  radicles  as 
methyl,  CH3,  or  ethyl,  C2H5.  They  are  called 
amines,  and  are  constituted  as  follows : 


PRELIMINARY  OUTLINE. 


289 


(H 

(CH3 

(CH, 

(CH3 

N4  H 

N.)  H 

N^  CH3 

N-!  CH3 

(H 

(H 

(H 

(CH3 

Ammonia. 

Methylamine. 

Dimethylamine. 

Trimethylamine. 

(C2H6 

(  C2H6 

(C2H6 

(CH3 

N-l  H 

N  \  C2H6 

N  \  C2H6 

N  \  C2H6 

(H 

IH 

(C2H5 

(  C2H6.   Etc. 

Ethylamine. 

Diethylamine. 

Triethylamine. 

Diethylmethylamine. 

Similarly,  from  PH3  we  get  a  series  of  phosphines ; 
from  AsH3,  arsines ;  from  SbH3,  stibines,  and  so  on. 
Compounds  of  this  kind  are  exceedingly  numerous, 
and  others  like  them  are  derived  from  ammonium, 
NH4: 


NH4C1. 


N(CH3)4C1. 


Ammonium  chloride.     Tetramethylammonium 
chloride. 


N(C.H.)«C1. 

Tetrethylammonium 
chloride. 


These  few  examples  will  suffice  for  present  pur- 
poses. 

One  other  noteworthy  feature  of  organic  com- 
pounds demands  a  brief  consideration  at  this  point 
— namely,  isomerism.  It  often  happens  that  two  or 
more  entirely  different  substances  are  represented 
by  the  same  formula,  both  containing  precisely  the 
same  elements,  united  in  precisely  the  same  pro- 
portions. Such  compounds  are  called  isoineric,  and 
owe  their  differences  to  different  groupings  of  the 
atoms  within  the  molecules.  Just  as  the  same  let- 
ters may  be  so  arranged  as  to  spell  several  differ- 
ent words,  so  the  same  atoms  may  be  grouped  in 
several  dissimilar  clusters.  For  example,  the  em- 
pirical formula  C2H6O  represents  two  substances 
—the  one  a  gas,  the  other  a  liquid.  One  is  the 
oxide  of  the  univalent  radicle  methyl,  the  other  is 
ethyl  hydroxide,  or  common  alcohol ;  and  their 


290  ORGANIC  CHEMISTRY. 

formulas,  written  side  by  side,  show  the  difference 

clearly : 

(CH3)2O.  C2H5OH. 

Methyl  oxide.  Alcohol. 

In  this  instance  both  compounds  have  the  same 
molecular  weight,  and  the  same  vapor  density.  In 
some  cases  of  imperfect  isomerism,  these  properties 
may  differ  in  such  a  way  that  the  compounds  may 
form  a  series  of  which  the  higher  members  shall 
have  molecular  weights,  even  multiples  of  the  low- 
est. Such  a  case  is  furnished  by  the  polymeric  series 
of  hydrocarbons  CnH2n,  in  which,  although  all  of 
its  members  have  the  same  percentage  composition, 
the  molecular  weights  vary  widely.  Another  ex- 
ample of  polymerism  is  afforded  by  the  compounds 
C2H2,  C6H6,  and  C8H8,  which  represent  three  differ- 
ent series.  Other  instances  of  isomerism  and  po- 
lymerism  will  be  considered  by-and-by. 


CHAPTER  XXXIII. 

CYANOGEN  AND  CARBONYL  COMPOUNDS. 

FREE  cyanogen,  C2N2  or  (CN)2,  is  prepared  by 
heating  mercuric  cyanide.  It  is  a  colorless  gas  with 
an  odor  resembling  peach-kernels,  and  it  burns  with 
a  beautiful  purple  flame.  In  the  chapter  upon  car- 
bon it  was  shown  that  this  gas  behaved  much  like 
an  element  of  the  chlorine  group,  and  that  the  mol- 
ecules (CN)2  and  C12  had  many  points  of  similarity. 
Thus  we  have  a  hydrocyanic  acid,  HCN,  and  a 
series  of  metallic  cyanides  such  as  KCN,  Hg(CN)2, 
and  so  on.  Some  of  these  compounds  have  practi- 
cal importance. 

Hydrocyanic  acid,  HCN,  commonly  known  as 
prussic  acid,  is  obtained  whenever  a  cyanide  is 
treated  with  a  strong  acid  like  sulphuric.  In  this 
respect  it  resembles  hydrochloric  acid,  as  the  sub- 
joined equations  show : 

H2SO4  +  2NaCl  =  2HC1.+  Na2SO4. 
H2SO4  +  2NaCN  =  2HCN  +  Na2SO4. 

Practically,  the  yellow  salt  known  as  potassium  fer- 
rocyanide  is  distilled  with  dilute  sulphuric  acid  in  a 
glass  retort,  and  an  aqueous  solution  of  hydrocyanic 
acid  is  collected  in  the  receiver.  This  acid  has  a 
strong  odor  resembling  peach-kernels  or  bitter-al- 


2Q2 


ORGANIC  CHEMISTRY. 


monds,  and  is  intensely  poisonous.  A  single  drop 
of  the  pure  compound,  which  is  a  volatile  liquid 
boiling  at  26.5°,  placed  upon  the  tongue  of  a  small 
animal,  such  as  a  cat  or  rabbit,  will  cause  death  al- 
most instantaneously.  It  is  the  most  sudden  and 
one  of  the  most  fatal  of  all  known  poisons,  and  its 
dangerous  qualities  are  shared  in  a  less  degree  by 
many  of  its  derivatives.  It  is  very  unstable,  and 
can  be  preserved  only  in  dilute  solutions.  As  an 
acid  it  is  exceedingly  weak,  and  may  be  expelled 
with  ease  from  most  of  its  compounds. 

Potassium  cyanide,  KCN,  is  a  white  salt  of  con- 
siderable importance.  Great  quantities  of  it  are 
used  in  the  processes  of  gold  and  silver  plating. 
It  is  dangerously  poisonous,  and  should  be  handled 
with  extreme  care.  It  has,  faintly,  the  characteris- 
•tic  peach-kernel  odor.  Silver  cyanide,  AgCN,  is  a 
white  precipitate  closely  resembling  the  chloride. 

With  some  of  the  metals  of  high  valency  cy- 
anogen forms  very  curious  and  important  double 
salts.  Of  these,  potassium  ferrocyanide,  K4Fe(CN)6, 
is  the  most  useful  and  noteworthy.  To  prepare 
this  salt,  iron-filings,  potash,  and  nitrogenous  mat- 
ter, such  as  scraps  of  horn,  hides,  leather-clippings, 
hair,  or  refuse  feathers,  are  heated  together  to  the 
temperature  of  fusion.  The  cooled  mass  is  after- 
ward treated  with  water,  and  the  solution  evapo- 
rated to  the  point  of  crystallization.  The  ferrocya- 
nide is  thus  obtained  in  large  yellow  crystals  con- 
taining three,  molecules  of  water.  It  is  sometimes 
called  the  "  yellow  prussiate  of  potash,"  and  is  not 
poisonous.  Its  uses  may  be  illustrated  by  experi- 
ment: 

EXPERIMENT   101. — To  a  solution  of  potassium 


CYANOGEN  AND  CARBON YL   COMPOUNDS.  293 

ferrocyanide  add  a  solution  of  ferrous  sulphate.  A 
pale-bluish  precipitate  will  form,  which  will  rapidly 
change  to  deep  blue.  Repeat  the  experiment,  using 
a  ferric  salt,  and  a  deep-blue  precipitate  will  be  pro- 
duced at  once. 

There  are  several  different  compounds  pro- 
ducible in  the  foregoing  manner.  One  of  them, 
Fe5(CN)12,  is  an  important  paint,  Prussian  blue  ;  and 
another,  derived  from  the  latter,  Fe7(CN)18,  is  called 
Williamson's  blue.  The  chief  use  of  potassium  fer- 
rocyanide is  in  the  manufacture  of  these  colors. 
With  solutions  of  copper,  potassium  ferrocyanide 
gives  a  very  characteristic  reddish-brown  precipi- 
tate ;  and  by  the  production  of  this,  very  small  traces 
of  copper  may  be  detected. 

Potassium  ferrocyanide  may  be  regarded  as  the 
potassium  salt  of  hydroferrocyanic  acid,  H4Fe(CN)6. 
This  acid  is  well  known,  and  forms  a  large  series  of 
salts.  Having  four  replaceable  hydrogen-atoms,  it 
is  tetrabasic.  In  none  of  the  ferrocyanides  do  the 
ordinary  tests  for  iron  reveal  the  presence  of  the 
later  metal.  It  is  completely  masked. 

By  passing  chlorine  into  a  solution  of  the  ferro- 
cyanide a  salt  called  potassium  ferricyanide  is  pro- 
duced. This  compound  forms  large  red  crystals 
having  the  formula  K3Fe(CN)6,  and  from  it  a  hydro- 
ferri cyanic  acid  and  a  series  of  corresponding  salts 
may  be  derived.  With  ferrous  solutions  potassium 
ferricyanide  gives  a  blue  precipitate,  but  in  ferric 
compounds  it  only  produces  a  slight  brownish  col- 
oration. It  is  a  useful  reagent  in  distinguishing  be- 
tween ferrous  and  ferric  compounds,  and  it  is  also 
employed  in  the  preparation  of  blue  paints.  Like 
iron,  cobalt  also  forms  interesting-  series  of  cobalto 


294 


ORGANIC  CHEMISTRY. 


and  cobalticyanides,  and  most  of  the  metals  of  the 
iron  and  platinum  groups  behave  in  a  similar  way. 
The  platinocyanides  are  among  the  most  beautiful 
compounds  known  to  chemistry. 

With  oxygen  and  sulphur,  cyanogen  forms  two 
quite  similar  acids — namely,  cyanic  acid,  CNOH, 
and  sulphocyanic  acid,  CNSH.  Potassium  sulpho- 
cyanate,  CNSK,  is  a  white  salt  which  yields  a  mag- 
nificent red  coloration  with  ferric  solutions.  It  gives 
no  reaction  with  ferrous  salts,  and  serves  as  a  very 
delicate  reagent  for  the  detection  of  ferric  iron. 

Some  of  the  cyanogen  compounds  display  in  a 
remarkable  degree  the  power  of  polymerization. 
For  example,  hydrocyanic  acid,  CNH,  readily 
changes  into  a  solid  compound,  C3N3H3,  called  tri- 
hydrocyanic  acid.  Cyanic  acid,  CNOH,  similarly 
is  related  to  cyanuric  acid,  C3N3O3H3,  and  to  a  third 
polymer  of  unknown  molecular  weight  called  cy- 
amelide.  So,  also,  there  are  two  chlorides  of  cyano- 
gen, one  a  liquid,  CNC1 ;  the  other  a  solid,  C3N3C13. 
On  account  of  this  tendency  to  polymerize,  the  de- 
rivatives of  cyanogen  are  very  numerous  and  com- 
plicated. 

When  ammonium  cyanate,  NH4CNO,  is  heated, 
its  atoms  undergo  a  peculiar  rearrangement,  and  it 
is  transformed  into  the  isomeric  compound,  carba- 
mide or  urea  : 


H2N 
H2N 

Ammonium  cyanate.  Carbamide. 


CN-0-NH4  =  CO\H2N 


The  latter  compound,  as  will  be  seen,  may  be  re- 
garded as  derived  from  two  atoms  of  ammonia,  by 
replacing  one  hydrogen-atom  from  each  by  the 
bivalent  radicle  CO.  This  radicle,  known  in  inor- 


CYANOGEN  AND  CARBON YL   COMPOUNDS. 


295 


ganic  chemistry  as  carbon  monoxide,  is  called  car- 
bonyl  for  brevity,  and  occurs  in  many  organic  com- 
pounds. Some  of  its  simpler  derivatives  are  as  fol- 
lows : 

co.o.        coo,        co<°£        co<*£- 

Carbonyl  oxide,  or       Carbonyl  Carbonic  acid.  Carbamic  acid, 

carbon  dioxide.  chloride. 

Carbamide  is  a  white  solid  which  is  found  in 
many  animal  juices,  and  has  great  theoretical  inter- 
est. It  was  the  first  organic  compound  ever  pro- 
duced by  synthesis  from  inorganic  matter.  It  acts 
like  a  weak  base,  uniting  with  nitric  and  oxalic  acids 
to  form  a  nitrate  and  an  oxalate,  and  it  also  yields 
many  complex  derivatives. 

If  we  heat  ammonium  sulphocyanate,  NH4CNS, 
instead  of  the  cyanate,  a  sulphocarbamide  or  sulpho- 
urea  will  be  formed. 

CN-S-NH*        =        CS<H*N 

Ammonium  sulphocyanate.  Sulphourea. 

This  compound  contains  the  radicle  sulphocarbonyl, 
CS,  which  yields  derivatives  similar  in  structure  to 
those  obtained  from  CO.     For  example  : 
COCla.  CSC12. 

Carbonyl  chloride.  Sulphocarbonyl  chloride. 

co/OH  cs/SH 

J\OH  ^\SH. 

Carbonic  acid.  Sulphocarbonic  acid. 

The  greater  number  of  these  compounds  are  in- 
teresting only  from  a  theoretical  point  of  view.  In 
the  present  instance  they  serve  to  illustrate  in  a  sim- 
ple way  the  convenience  of  structural  formulae.  By 
means  of  the  latter,  many  relations  between  different 
substances  may  be  most  clearly  brought  out,  and  the 
memory  can  thus  be  aided  to  a  wonderful  degree. 


\ 


CHAPTER  XXXIV. 

THE   METHANE   SERIES. 

THE  methane  or  marsh-gas  series  of  hydrocar- 
bons, CnH2n  +  2,  is  of  the  utmost  importance,  both 
in  theory  and  in  practical  work.  Some  of  its  mem- 
bers constitute  the  greater  part  of  petroleum  ;  and 
from  other  members  such  noteworthy  substances  as 
alcohol,  ether,  chloroform,  and  acetic  acid,  are  de- 
rived. Structurally,  the  series  is  very  simple,  the 
carbon-atoms  forming  a  regular  chain  around  which 
the  hydrogen-atoms  are  symmetrically  arranged. 
A  very  few  formulas  will  serve  for  illustration  : 

Methane,  CH4.  Ethane,  C2H8.         Propane,  C3H8.  Butane,  C4H10. 

H  H  H  H 

H-C-H  H-C-H  H-C-H  H-C-H 

H  H-C-H  H-C-H  H-C-H 

H  H-C-H  H-C-H 

H  H-C-H 

i 
H 

And  so  on,  regularly,  up  to  C^H^.  After  butane 
the  hydrocarbons  of  this  series  receive  numerical 
names,  based  upon  the  number  of  carbon-atoms 
which  they  contain.  Thus,  C5H12  is  pentane,  C6H14 
is  hexane,  C7H16  is  heptane,  C^H^  is  decane,  etc. 
In  properties,  these  hydrocarbons  vary  regularly. 


THE  METHANE  SERIES.  297 

Methane,  which  was  described  under  carbon,  is  a 
gas,  and  ethane,  propane,  and  butane  are  also  gase- 
ous. Pentane  is  a  liquid  boiling  at  38°,  hexane  boils 
at  70°,  and  so  on  through  a  series  of  liquids  growing 
less  and  less  volatile  as  we  ascend,  until  at  last  we 
come  to  solid,  waxy  compounds  which  are  known  as 
paraffins.  The  whole  series  is  sometimes  called  the 
paraffin  group.  Paraffin  itself,  such  as  is  used  for 
making  candles,  is  a  mixture  of  these  higher  hydro- 
carbons ;  coal-oil,  or  petroleum,  consists  chiefly  of 
the  liquid  members  of  the  series.  The  latter  are 
separated  by  a  process  of  distillation,  and  the  mixt- 
ure which  distills  over  at  comparatively  low  tem- 
peratures is  known  as  naphtha  or  gasoline.  Above 
170°.  the  distillate  is  used  for  illuminating  oil  or 
kerosene ;  higher  still,  heavier  and  denser  products 
are  obtained,  which  serve  for  lubricating  machinery. 
Kerosene  which  has  not  been  carefully  freed  from 
the  more  volatile  hydrocarbons  is  dangerous,  and 
none  should  be  used  which  gives  off  inflammable 
vapor  at  temperatures  below  110°  Fahr.  Such  va- 
pors, like  fire-damp,  form  explosive  mixtures  with  air. 
If,  by  proper  reactions,  we  replace  one  atom  of 
hydrogen  in  each  of  the  foregoing  hydrocarbons  by 
a  hydroxyl  group,  -O-H,  we  shall  obtain  a  series  of 
most  important  compounds  which  are  called  alco- 
hols. Thus : 


OH 

OH 

OH 

i 

i 

i 

H-C-H 

H-C-H 

H-C-H 

i 

i 

i 

H 

H-C-H 

H-C-H 

CH4O,  methyl  alcohol. 

i 

i 

H 

H-C-H 

CaH6O,  ethyl  alcohol. 

i 

H 

C3H8O,  propyl  alcohol. 


298  ORGANIC  CHEMISTRY. 

And  so  on  through  the  series.  These  alcohols  may 
be  conveniently  regarded  as  the  hydroxides  of  cer- 
tain radicles,  of  which  methyl,  CH3,  ethyl,  C2H5,  and 
amyl,  C5Hn,  are  the  most  commonly  encountered. 
These  radicles  do  not  exist  in  the  free  state,  but 
their  derivatives  are  of  the  highest  importance  ;  and 
most  of  them  may  be  easily  compared  with  the  com- 
pounds of  the  univalent  metals.  Thus : 

KOH.  CH3OH.  CaH6OH.  C5HnOH.     Etc. 

K2O.  (CH8)aO.  (C2H5)2O.  (CBHn)2O.       " 

KC1.  CH3C1.  C2H6C1.  C»H,iCl. 

KNO3.  CH3NO3.  C2H6NO3.  C6HnNO8.      " 

These  alcoholic  salts  are  mostly  liquids,  and  are 
called  ethers.  Their  names,  except  in  the  series  of 
alcohols,  are  precisely  like  those  used  in  inorganic 
chemistry — as,  for  example,  methyl  chloride,  ethyl 
oxide,  propyl  nitrate,  amyl  sulphate,  etc.  Nearly 
every  acid,  organic  or  inorganic,  can  unite  with 
these  radicles  to  form  such  ethers. 

Three  of  the  alcohols — namely,  those  of  methyl, 
ethyl,  and  amyl — have  practical  importance,  and 
therefore  deserve  especial  mention.  Methyl  alco- 
hol, CH3OH,  commonly  called  wood-spirit,  is  a 
colorless  liquid  obtained  by  the  dry  distillation  of 
wood.  The  latter,  when  distilled  at  a  high  tempera- 
ture, yields  a  variety  of  liquid  products,  and  from 
the  mixture  methyl  alcohol  may  be  separated.  It 
has  a  specific  gravity  of  .814,  and  boils  at  55°,  and  is 
used  partly  as  a  cheaper  substitute  for  common  alco- 
hol in  various  manufacturing  processes,  and  partly 
in  the  preparation  of  certain  of  the  aniline  colors. 

Ethyl  alcohol,  C2H5OH,  is  the  compound  of 
this  series  to  which  in  common  life  the  name  of 


THE  METHANE  SERIES.  299 

alcohol  is  especially  applied.  Although  it  may  be 
obtained  from  ethane,  it  is  practically  prepared  only 
by  the  fermentation  of  saccharine  and  starchy  bodies, 
such  as  cane-sugar,  glucose,  and  the  starch  of  pota- 
toes or  grain.  These  compounds,  dissolved  in  wa- 
ter, are  fermented  by  yeast,  and  a  weak  solution  of 
alcohol  is  thus  obtained.  The  latter  is  then  concen- 
trated by  distillation,  the  process  being  repeated 
until  an  alcohol  containing  only  about  10  per  cent 
of  water  passes  over.  To  obtain  pure  or  "  absolute  " 
alcohol  the  commercial  product  is  again  distilled 
over  caustic  lime,  which  serves  to  retain  the  water. 

EXPERIMENT  102. — Mix  alcohol  and  water  in 
equal  proportions,  place  the  mixture  in  a  glass  re- 
tort, and  distill  until  one  half  has  passed  over  into 
the  receiver.  Inasmuch  as  alcohol  boils  at  78.4°  and 
water  at  100°,  the  distillate  will  be  found  to  contain 
most  of  the  alcohol,  while  the  portion  remaining  in 
the  retort  will  be  mainly  water.  Now  repeat  the 
operation  with  the  distillate,  again  distilling  one  half, 
and  a  still  stronger  alcohol  will  be  obtained.  This 
process,  which  is  known  as  fractional  distillation,  is 
continually  employed  in  the  laboratory  for  separating 
liquids  of  different  volatility.  The  most  volatile  dis- 
till first,  the  least  volatile  remaining  longest  behind. 

Pure  alcohol  is  a  colorless,  inflammable  liquid  of 
specific  gravity  .806.  It  boils  at  78.4°,  but  has  never 
been  frozen;*  hence  its  use  in  thermometers  in- 
tended for  registering  temperatures  below  the  freez- 
ing-point of  mercury.  It  has  a  peculiar  spirituous 
smell  and  a  burning  taste,  and  in  the  pure  state  is 
poisonous.  In  a  diluted  condition  it  is  used  as  a 

*  Since  this  paragraph  was  written,  alcohol  has  been  frozen.     At  — 
130.5°  C.,  it  solidifies  to  a  white  mass. 


300 


ORGANIC  CHEMISTRY. 


stimulant,  and  it  is  the  intoxicating  principle  of  all 
wines,  spirits,  and  malt-liquors.  Beer  and  ale  contain 
from  4  to  7  per  cent  of  alcohol  ;  wine  from  6  to  20 
per  cent  ;  rum,  brandy,  and  whisky  from  40  to  50  per 
cent.  The  stronger  commercial  alcohol,  or  spirits  of 
wine,  contains  from  50  per  cent  upward,  and  is  used 
as  an  antiseptic,  as  a  burning-fluid,  as  a  solvent  for 
gums  and  resins,  in  the  manufacture  of  varnishes,  per- 
fumery, and  medicinal  preparations,  and  for  a  great 
variety  of  other  practical  purposes.  To  the  chemist 
it  is  one  of  the  most  useful  of  chemical  substances. 

Amyl  alcohol,  C5HnOH,  occurs  as  an  impurity 
in  spirits  distilled  from  potatoes.  It  is  commonly 
known  as  the  chief  constituent  of  a  disagreeable 
mixture  called  fusel-oil.  When  pure,  amyl  alcohol 
is  a  colorless  liquid  which  boils  at  131°,  and  has  a  pe- 
culiarly suffocating  odor.  It  is  used  in  the  prepara- 
tion of  valeric  acid  and  some  of  its  ethers.* 

Propyl  alcohol,  C3H7OH,  and  butyl  alcohol, 
C4H9OH,  lie  between  ethyl  and  amyl  alcohols. 
Cetyl  alcohol,  QeHggOH,  is  a  solid  compound 
derived  from  spermaceti  ;  and  melissyl  alcohol, 
CsoHflOH,  is  one  of  the  constituents  of  beeswax. 
Like  the  higher  hydrocarbons  of  the  methane  series, 
the  higher  alcohols  and  their  derivatives  are  solid. 

When  common  alcohol  is  cautiously  mixed  with 
strong  sulphuric  acid,  a  compound  known  as  ethyl- 
sulphuric  acid  is  formed.  This  is  the  type  of  a 
series  of  acids,  constituted  as  follows  : 


Sulphuric.     Methylsulphuric.     Ethylsulphuric.    Propylsulphuric.     Amylsulphuric. 

etc. 
*  See  next  chapter. 


THE  METHANE  SERIES. 


301 


Heated  with  an  additional  quantity  of  alcohol,  ethyl- 
sulphuric  acid  undergoes  a  further  change,  and  ethyl 
oxide  is  formed.  At  the  same  time  sulphuric  acid 
is  reproduced,  ready  to  act  upon  a  fresh  portion  of 
alcohol  ;  thus  : 


x  o  _u     x  ^o 

/  H  //  ^^4* 

These  reactions  are  applied  on  a  large  scale  to  the 
manufacture  of  ethyl  oxide,  which  is  commonly 
known  as  ether.*  This  is  a  colorless  liquid  of  pecul- 
iar odor,  specific  gravity  .74,  and  boiling-point  34.5°. 
Its.  chief  and  important  use  as  an  anaesthetic,  for 
preventing  the  pain  of  surgical  operations,  is  well 
known.  Allied  to  it  are  other  ethereal  oxides,  which 
the  subjoined  formulae  may  serve  to  illustrate  : 

CH3\  C2H5\  C6Hn\  CH8  x  C2H6  x 

CH8/L          C2H5/U         C6Hn/L          C2H5/U        C5Hn/U> 

Methyl  ether.      Ethyl  ether.  Amyl  ether.  Methylethyl  Ethylamyl 

ether.  ether. 

The  fourth  and  t  fifth  of  these  formulae  represent 
mixed  ethers.  Many  such  compounds  are  possible. 
Besides  these  there  are  similar  bodies  containing 
sulphur,  most  of  which  are  liquids  of  exceedingly 
nauseous  odor.  Their  derivation  may  be  illustrated 
thus: 


Ethyl  sulphide.  Amyl  sulphide.     Ethyl  hydrosulphide.    Amyl  hydrosulphide. 

The  hydrosulphides  resemble  the  alcohols  in  struct- 
ure, and  are  called  mercaptans. 

*  Erroneously  called  "  sulphuric  ether  "  in  commerce.     The  true 
sulphuric  ether  is  ethyl  sulphate,  (Ca 


302  ORGANIC  CHEMISTRY. 

By  the  action  of  hydrochloric  acid  on  the  alco- 
hols, the  chlorides  of  the  corresponding  radicles  may 
be  produced.  With  bromine  and  iodine,  in  pres- 
ence of  a  little  phosphorus,  the  alcohols  yield  simi- 
lar bromides  and  iodides.  Methyl  chloride,  CH3C1, 
is  a  gas ;  but  the  other  chlorides,  bromides,  and 
iodides  of  the  commoner  radicles  of  this  series  are 
volatile  liquids  resembling  chloroform  in  odor. 
These  compounds  are  often  of  use  as  steps  in  the 
preparation  of  others. 

When  methyl  or  ethyl  alcohol  is  heated  with 
bleaching-powder,  chloroform  is  produced.  This 
compound,  CHC13,  is  a  clear  liquid  of  specific  grav- 
ity 1.52,  and  an  agreeable  smell.  It  boils  at  62°. 
Like  ether,  it  is  an  important  anaesthetic,  but  is  less 
safe.  lodoform,  CHI3,  is  a  yellow  solid  of  some 
value  in  medicine.  Both  of  these  compounds  are 
simple  derivatives  of  methane  : 

H  Cl  I 

H-C-H  H-C-C1  H-C-I. 

i  i  i 

H  Cl  I 

Methane.  Chloroform.          '  lodoform. 


CHAPTER   XXXV. 

THE   FATTY  ACIDS. 

BY  the  action  of  oxidizing  agents  upon  the  fore- 
going alcohols,  two  new  series  of  compounds  may 
be  obtained.  The  reactions,  with  any  given  alcohol, 
are  as  follows :  First,  two  atoms  of  hydrogen  are 
withdrawn,  forming  water,  and  leaving  a  compound 
called  an  aldehyde : 

C2H6O  +  O  =  CaH4O  +  H3O. 

By  further  oxidation  the  aldehyde  takes  up  an  atom 
of  oxygen,  and  an  acid  is  produced : 

CaH4O  +  O  =  C2H4O3. 

The  relations  of  these  sets  of  compounds  to  each 
other,  and  to  the  methane  series,  may  be  repre- 
sented structurally : 


H 

OH 

H 

OH 

i 

i 

i 

i 

H-C-H 

H-C-H 

C  =  0 

c=o 

i 

i 

r 

1 

H 

H 

H 

H 

Methane. 

Methyl  alcohol. 

Formaldehyde. 

Formic  acid. 

H 

OH 

H 

OH 

i 

i 

i 

i 

H-C-H 

H-C-H 

C  =  0 

c=o 

i 

i 

i 

1 

H-C-H 

H-C-H 

H-C-H 

H-C-H 

i 

i 

i 

i 

H 

H 

H 

H 

Ethane. 

Ethyl  alcohol. 

Acetaldehyde. 

Acetic  acid. 

14 


304  ORGANIC  CHEMISTRY. 

Thus,  corresponding  to  every  hydrocarbon  in  the 
methane  series,  we  have  an  alcohol,  an  aldehyde  (al- 
cohol  ^v^/rogenatum),  and  an  acid.  The  aldehydes 
are  quite  unstable  bodies,  and  the  one  derived  from 
common  alcohol  is  the  best  known.  It  is  a  very 
volatile  liquid,  having  a  peculiar  odor,  which  may 
be  recognized  whenever  alcohol  is  dropped  upon 
chromic  acid.  Its  uses  are  few. 

The  acids  of  this  series,  however,  are  important. 
The  lower  members  are  volatile  liquids,  the  higher, 
above  QoH^Oa,  are  waxy  or  greasy  solids.  Inas- 
much as  some  of  them  are  essential  constituents  of 
fats  and  oils,  the  entire  series  has  been  named  the 
fatty  acids.  The  more  important  among  them  are 
the  following : 

Formic      acid,  CH2O2,      or  HCOOH.  Boils  at  100°. 


Acetic          " 

C2H4O2, 

"  CHsCOOH. 

"      "  1  1  8°. 

Propionic     " 

C8H602, 

"  CaH6COOH. 

"      "  140°. 

Butyric        " 

C4H8O3, 

"  C8H7COOH. 

"      "  163°. 

Valeric 

C5H10Oa, 

"  C4H9COOH. 

"      «  185°. 

Stearic         " 

Ci8H36O2, 

"  Ci7H86COOH. 

Melts  at    69°. 

In  each  of  these  acids  we  find  the  group  COOH, 
or,  in  detail,  O=C— OH,  which  is  characteristic  of 
organic  acids.  In  monobasic  acids  like  these,  it 
occurs  once  ;  in  bibasic  acids,  twice  ;  in  tribasic 
acids,  three  times,  etc.  In  the  formation  of  salts 
from  these  acids,  it  is  only  the  hydrogen  of  the 
COOH  group  which  is  replaceable  by  metals  or  by 
bases. 

Several  of  the  fatty  acids  are  important,  either 
by  themselves  or  in  their  salts  or  ethers.  Stearic, 
margaric,  and  palmitic  acids,  are  especially  useful 
in  fats,  oils,  and  soaps,  and  will  be  considered  in 


THE  FATTY  ACIDS. 


305 


another  chapter.     Acetic  acid,  or  vinegar,  merits  a 
detailed  notice  here.     It  is  commonly  prepared  by 


FIG.  52. — Manufacture  of  Vinegar. 

the  oxidation  of  dilute  alcohol,  such  as  cider,  wine, 
or  weak  whisky.  In  cider  and  wine  the  alcoholic 
stage  of  fermentation  is  followed  by  an  acetous  stage, 
and  the  change  from  alcohol  to  acetic  acid  takes 
place  without  artificial  assistance.  This  transforma- 
tion of  cider  into  vinegar  is  a  matter  of  every-day 
observation ;  but  only  a  small  part  of  the  vinegar  in 
use  is  made  in  this  way.  On  a  large  scale,  very 
weak  alcohol,  such  as  the  fermented  mash  from 
which  spirit  is  to  be  distilled,  is  allowed  to  trickle 
slowly  through  large  casks  filled  with  wood-shav- 
ings. The  alcohol,  diffused  over  the  shavings,  ex- 
poses a  very  large  surface  to  the  oxidizing  action  of 
the  air,  which  latter  enters  the  cask  freely  through 
holes  in  the  sides,  and  escapes  through  other  holes 
in  the  top.  The  oxidation  from  alcohol  to  acetic 
acid  is  thus  effected  much  more  rapidly  than  by  the 
tedious  process  of  fermentation  which  was  previ- 
ously referred  to. 


3o6  ORGANIC  CHEMISTRY. 

EXPERIMENT  103. — Distill  a  little  vinegar  from  a 
glass  retort.  The  distillate  will  be  a  weak  acetic 
acid  free  from  the  impurities  which  gave  the  vine- 
gar its  color.  Pure  acetic  acid  may  be  prepared  by 
distilling  an  acetate  with  sulphuric  acid.  A  sul- 
phate will  be  formed  and  acetic  acid  set  free. 

Perfectly  pure  acetic  acid  is  a  colorless  liquid 
which  solidifies  to  an  ice-like  mass  at  17°.  It  has 
the  odor  of  vinegar  to  an  increased  degree,  and  has 
all  the  properties  of  a  strong  acid.  Dissolve  sodium 
or  calcium  carbonate  in  vinegar,  and  you  will  obtain, 
with  vigorous  effervescence,  a  solution  of  sodium  or 
calcium  acetate.  Sodium  acetate  is  a  useful  labora- 
tory reagent ;  lead  acetate  is  the  well-known  "  sugar 
of  lead";  copper  acetate  is  "verdigris."  These 
salts  (omitting  water  of  crystallization)  are  formed 
from  acetic  acid  by  substitution  of  hydrogen,  pre- 
cisely as  in  the  domain  of  inorganic  chemistry. 

Thus  : 

Acetic  acid,  C2H4Oa. 

Sodium       acetate,  C3H8OaNa. 
Potassium       "         CaH3OaK. 
Lead  "       (C3H3O2)aPb. 

Copper  "       (C2HsOa)aCu. 

With  the  alcohols  of  the  methane  series  the  fatty 
acids  yield  a  large  number  of  compound  ethers. 
These  are  interesting,  both  because  of  their  proper- 
ties and  on  account  of  their  bearing  upon  the  sub- 
ject of  isomerism.  Practically,  several  of  them  are 
made  for  use  in  the  manufacture  of  flavoring  ex- 
tracts. For  instance,  ethyl  butyrate  has  the  taste 
and  odor  of  pineapples;  amyl  acetate  affords  a 
close  imitation  of  bananas ;  amyl  valerate  is  made 
as  "  apple-oil,"  etc.  The  peculiar  flavors  of  many 


THE  FATTY  ACIDS.  307 

fruits  are  doubtless  due  to  the  existence,  naturally 
formed,  of  some  of  these  same  ethers.  Each  ether 
is  isomeric  with  one  of  the  acids,  and  in  some  cases 
several  ethers  are  isomeric  with  each  other.  The 
cause  of  the  isomerism,  however,  is  easily  under- 
stood, as  the  following  formulae  for  the  compounds 
C7H14O2  will  show  : 

(Enanthylic  acid,  C6Hi3,  COOH  =  C7H14Oa. 

Hexyl  formate,  CeHu,  CHO2  = 

Amyl  acetate,  CBHn,  C2H3Oa  = 

Butyl  propionate,  C4H9,  C3H5O2  = 

Propyl  butyrate,  C3H7,  C4H7O2  = 

Ethyl  valerate,  C2H6,  C5H9O2  = 

Methyl  caproate,  CH3,  C6HnO2  = 

In  these  ethers  the  hydrocarbon  radicles  replace 
hydrogen-atoms  exactly  as  if  they  were  univalent 
metals.  If  the  first  compound  in  the  column,  which 
is  an  acid,  is  treated  with  a  solution  of  caustic  soda, 
its  sodium  salt  is  formed  and  water  is  set  free.  The 
second  compound,  similarly  treated,  would  give  so- 
dium formate  and  hexyl  alcohol ;  the  third,  sodium 
acetate  and  amyl  alcohol ;  the  fourth,  sodium  pro- 
pionate and  butyl  alcohol,  etc.  So  then,  although 
the  seven  compounds  have  the  same  percentage 
composition  and  molecular  weight,  it  is  easy  to 
demonstrate  experimentally  that  they  differ  in  chemi- 
cal structure,  and  to  show  wherein  the  differences 
lie.  Some  cases  of  isomerism  are  less  easily  ex- 
plained ;  but  all  are  explainable  in  some  such  gen- 
eral way. 

If  from  acetic  acid,  C2H4O2,  we  withdraw  a  hy- 
droxyl  group,  OH,  a  compound  radicle  called  acetyl, 
C2H3O,  will  remain.  This  radicle  does  not  exist  in 
the  free  state,  but  some  of  its  compounds  are  inter- 


308  ORGANIC  CHEMISTRY. 

esting.  Thus,  it  forms  a  chloride,  C2H3OC1,  which 
is  well  known,  and  several  amides.  These  resemble 
the  amines,  with  this  difference,  that  whereas  in  the 
latter  compounds  the  hydrogen  of  ammonia  is  re- 
placed by  basic  or  positive  radicles,  in  the  amides 
the  replacement  is  effected  by  acid  or  negative 
groups.  Thus : 

(  C3H6  (  C2HB  (  C2H6 

N  •]  H  N  \  C2H6  N  \  C2H6 

(  H  (  H  (  C2H6 

Ethylamine.  Diethylamine.  Triethylamine. 

(  C2H3O        (  C2H3O         (  C2H3O 

N  1  H          N  1  C2H30       N  4  C2H30 

(  H  (  H  (  C2H3O. 

Acetamide.  Diacetamide.  Triacetamide. 

From  the  other  acids  of  the  series,  by  withdrawal 
of  hydroxyl,  other  acid  radicles  are  formed ;  and 
these  have  properties  similar  to  acetyl.  The  amines 
are  all  strong  bases,  the  amides  are  neutral  or  acid. 
By  the  action  of  chlorine  upon  acetic  acid,  three 
substitution  acids  may  be  obtained.  All  are  strong 
acids,  and  yield  important  derivatives: 

C2H4O3,       acetic  acid. 
C2H3C1O2,   monochloracetic  acid. 
C2H2C12O2,  dichloracetic  " 

C2HC13O2,   trichloracetic          " 

The  fourth  atom  of  hydrogen  belongs  to  the  COOH 
group,  and,  although  replaceable  by  metals,  can  not 
be  replaced  by  chlorine.  This  fact  adds  to  the  proof 
that  it  is  differently  combined  from  the  others.  Just 
as  aldehyde  is  related  to  acetic  acid,  so  also  there  is 
a  trichloraldehyde  related  to  trichloracetic  acid.  It 
is  a  liquid  of  formula  C2HC13O,  and  is  more  briefly 
known  as  chloral.  It  combines  with  water  to  form 


THE  FATTY  ACIDS. 


309 


a  solid  crystalline  hydrate  which  is  much  used  in 
medicine  for  producing  quiet  sleep. 

One  other  compound  may  be  noticed  here  as 
the  type  of  an  important  class.  Whenever  an  ace- 
tate is  subjected  to  dry  distillation,  a  volatile  liquid 
called  acetone  is  formed.  This  compound,  C8H6O, 
is  the  first  of  a  large  series,  members  of  which  may 
be  obtained  by  a  variety  of  reactions.  They  are  all 
known  as  ketones,  and  are  structurally  formed  by 
the  union  of  two  univalent  radicles  with  bivalent 
carbonyl,  CO.  Acetone  may  be  called  dimethyl- 
ketone  : 

CHS  CH3  CaH* 

i  i  i 

c=o  c=o  c=o 

CHs  CaH6  CaH6        Etc. 

Dimethyl-ketone.          Ethylmethyl-ketone.  Diethyl-ketone. 

The  ketones  are  isomeric  with  the  aldehydes,  but 
have  entirely  different  constitution. 


CHAPTER  XXXVI. 

THE   OLEFINES. 

THE  CnH2n  series  of  hydrocarbons  is  known  as 
the  olefine  series,  from  "  olefiant  gas  "  or  ethylene, 
its  first  member.  Some  of  its  relations  to  the  me- 
thane series  and  to  the  alcohol  radicles  are  indicated 
in  the  following  formulas  and  the  accompanying 
nomenclature  : 

O Han + a.  Ale.  radicles*  OH an. 

CH4,  methane.  CH3,  methyl.  CH2,  methylene.* 

CaH6,  ethane.  CaH8,  ethyl.  CaH4,  ethylene. 

CsH8,  propane.  C3H7,  propyl.  C3H8,  propylene. 

C4Hio,  butane.  C4H9,  butyl.  C4H8,  butylene. 

CeHia,  pentane.  C5HU,  amyl.  C6Hi0,  amylene. 

C8Hu,  hexane.  C6Hi3,  hexyl.  CeHia,  hexylene. 

C7Hi6,  heptane.  C7Hi6,  heptyl.  C7Hi4,  heptylene. 

CsHis,  octane.  C8Hi7,  octyl.  C8Hi6,  octylene,  etc. 

The  most  important  one  of  these  olefines  is  ethylene, 
which  has  already  been  described  as  a  constituent 
of  coal-gas.  In  it  the  two  carbon-atoms  are  united 
by  a  double  bond  of  affinity,  as  shown  in  the  sub- 
joined formula.  The  second  formula  is  merely  a 
convenient  abbreviation  of  the  first. 


H-C-H  C  =  Ha 

ii  or  ii 

H-C-H  OHa. 

*  Known  only  in  compounds  ;  can  not  exist  free. 


THE  OLEFINES.  3  1  1 

These  defines  all  behave  as  if  they  were  biva- 
lent radicles.  Each  one  unites  with  two  chlorine- 
atoms  to  form  a  chloride,  one  oxygen-atom  to  form 
an  oxide,  etc.  They  also  take  up  two  hydroxyl 
groups  to  form  a  series  of  alcohols,  which  are  some- 
what better  known  as  glycols.  In  all  these  deriva- 
tives, however,  the  carbon-atoms  are  united  by  a 
single  bond  only,  the  other  bond,  which  is  fixed  in 
the  hydrocarbons  themselves,  being  released  to  new 
uses.  Thus  : 


C=Ha.  C  =  H3C1.  OH3OH. 

Ethylene.  Ethylene  chloride.  Ethylene  alcohol. 
CnHaNOa                         OH2C2H3Oa  C  =  Ha 

'  i  i  \O 


Ethylene  nitrate.  Ethylene  acetate.  Ethylene  oxide. 

By  the  action  of  oxidizing  agents  the  alcohols  of 
the  olefine  series,  like  the  alcohols  of  the  methane  se- 
ries, yield  acids.  Only,  instead  of  a  single  set  of  acids, 
each  glycol  yields  two  such  derivatives.  Thus  : 

CH2OH  CH2OH  COOH 

i  i  i 

CH2OH.  COOH.  COOH. 

Ethylene  alcohol.  Glycollic  acid.  Oxalic  acid. 

Glycollic  acid  and  its  homologues,  having  but  one 
COOH  group,  are  monobasic  ;  the  acids  of  the  ox- 
alic series,  on  the  other  hand,  are  bibasic  : 

CH2OH          COOH          COOK 
COOK.          COOK.          COOK. 

Potassium  Hydrogen  potas-  Neutral  potas- 

glycollate.  sium  oxalate.  sium  oxalate. 

Some  of  these  acids  and  their  derivatives  are 
compounds  of  very  great  importance.  In  the  gly- 
collic  series,  for  instance,  we  find  lactic  acid,  which 


312  ORGANIC  CHEMISTRY. 

is  the  acid  of  sour  milk ;  while  from  oxalic  acid  the 
more  important  acids  of  various  natural  fruits  may 
be  rationally  derived. 

Lactic  acid,  C3H6O3,  may  be  regarded  as  derived 
from  glycollic  acid,  C2H4O8,  by  the  addition  of  CH2. 
In  reality,  an  atom  of  hydrogen  in  glycollic  acid  is 
replaced  by  a  methyl  group,  CH3.  This  is  equiva- 
lent to  adding  CH2,  and  all  homologous  series, 
either  of  hydrocarbons  or  of  their  derivatives,  are 
built  up  by  this  process  of  substitution.  Lactic 
acid  is  a  sirupy  liquid,  having  a  specific  gravity  of 
1.215,  and  is  easily  decomposed  by  heat.  It  may 
be  formed  synthetically,  but  it  is  generally  prepared 
from  sour  milk.  When  the  latter  is  used  in  cookery, 
the  free  acid  is  neutralized  by  sodium  bicarbonate, 
and  a  soluble  lactate  of  sodium  is  produced.  Sev- 
eral of  the  lactates  are  used  medicinally,  and  all  of 
them  are  soluble  in  water.  A  baking-powder  con- 
taining lactic  acid  has  recently  been  patented. 

Oxalic  acid,  H2C2O4,  is  found  in  the  juice  of  cer- 
tain plants,  such  as  the  sorrel  and  rhubarb.  It  may 
be  prepared  synthetically  by  a  variety  of  methods, 
but  on  a  commercial  scale  only  two  processes  are 
used.  One  of  these  may  be  verified  experimentally : 

EXPERIMENT  104. — Pour  strong  nitric  acid  over 
a  few  grammes  of  white  sugar  contained  in  a  large 
flask  or  beaker.  When  the  action  has  ceased,  and 
red  fumes  are  no  longer  given  off,  evaporate  the  liq- 
uid to  a  small  bulk.  On  cooling,  oxalic  acid  will  crys- 
tallize out.  Starch  may  be  used  instead  of  sugar. 

The  second  process,  which  is  cheaper,  and  which 
of  late  years  has  quite  supplanted  the  first,  is  as 
follows:  When  sawdust  is  heated  with  caustic  pot- 
ash, potassium  oxalate  is  formed.  This,  treated 


THE  OLEFINES. 


313 


with  milk  of  lime,  yields  an  insoluble  calcium  ox- 
alate.  The  latter,  treated  with  sulphuric  acid,  gives 
calcium  sulphate,  while  oxalic  acid  is  set  free,  and 
may  be  purified  by  recrystallization. 

Oxalic  acid  is  readily  soluble,  and  crystallizes 
with  two  molecules  of  water  in  prisms  which  re- 
semble Epsom  salt.  It  is  intensely  sour,  a  very 
strong  acid,  and  quite  poisonous.  Chalk  or  mag- 
nesia, suspended  in  water,  neutralizes  the  acid,  and 
is  a  good  antidote  in  cases  of  poisoning.  In  the 
household,  oxalic  acid  is  often  used  for  removing 
ink-stains  or  iron-rust  from  linen  or  clothing.  As, 
however,  the  acid  attacks  the  fiber  of  the  cloth,  it 
should  be  washed  out  as  soon  as  it  has  produced 
the  desired  bleaching  effect.  The  oxalic  acid  which 
was  made  in  Experiment  104  may  be  used  for  veri- 
fying its  solvent  property,  either  upon  a  rag  spotted 
w^ith  ink  or  upon  a  sheet  of  written  paper.  On  a 
large  scale,  oxalic  acid  is  used  by  calico-printers  as 
a  means  of  discharging  certain  colors. 

Oxalic  acid  is  the  first  term  of  a  long  homologous 
series.  The  second  term,  malonic  acid,  C3H4O4,  is 
unimportant ;  but  the  third  member,  succinic  acid, 
C4H6O4,  is  interesting.  This  acid  is  obtained  from 
amber,  and  is  noteworthy  on  account  of  its  struct- 
ural relations  to  two  fruit-acids,  malic  and  tartaric. 

Succinic  acid,  C4H6O4. 
Malic         "      C4H(,O6. 
Tartaric    "      C4H8Ofl. 
COOH  COOH  COOH 

CHa  CHOH          CHOH 

CHa  CHa  CHOH 

COOH.          COOH.         COOH. 

Succinic  acid.  Malic  acid.  Tartaric  acid. 


314  ORGANIC  CHEMISTRY. 

Malic  acid  is  the  acid  of  apples,  pears,  and 
eral  other  fruits  and  vegetables.  It  is  a  white,  crys- 
talline body,  which  may  be  derived  from  succinic 
acid  by  artificial  means,  but  is  more  cheaply  pre- 
pared from  mountain-ash  berries.  Tartaric  acid  is 
the  acid  of  grapes,  and  has  considerable  practical 
importance.  During  the  fermentation  of  wine  its 
potassium  salt  is  deposited  in  an  impure  condition 
on  the  sides  of  the  wine-casks,  and  from  this  crude 
tartar  the  acid  itself  may  be  obtained.  It  has  also 
been  prepared  synthetically  from  succinic  acid. 

Tartaric  acid  occurs  in  white  crystals  *  having  an 
intensely  sour  taste.  It  is  readily  soluble  in  water, 
and  its  solution  effervesces  strongly  with  carbonates. 
In  Seidlitz  or  Rochelle  powders  it  forms  the  con- 
tents of  the  smaller  papers,  while  the  other  papers 
contain  a  mixture  of  sodium  hydrogen  carbonate 
and  a  tartrate  known  as  Rochelle  salt.  The  acid  is 
also  used  in  the  preparation  of  a  variety  of  efferves- 
cent drinks,  and  by  calico-printers  as  a  discharge 
for  certain  mordants. 

There  are  two  sets  of  tartrates,  a  neutral  and 
an  acid  series,  and  some  of  these  salts  are  practically 
important.  They  may  be  represented  in  their  rela- 
tions to  the  acid  by  condensed  formulas  like  the  fol- 
lowing : 

C4H406.        ^     C4H406.        £     C4H408.        ^a     C4H40«. 


Tartaric  acid.  Hydrogen  potas-  Potassium  Rochelle  salt. 

sium  tartrate.  tartrate. 

The  acid  potassium  tartrate  is  the  well-known 
cream  of  tartar,  which  is  much  used  in  cookery,  and 
as  an  ingredient  of  baking-powders.  With  a  few 

*  Commercial  tartaric  acid  occurs  oftener  as  a  white  powder  than  it 
does  in  the  form  of  crystals. 


THE  OLEFINES.  3x5 

exceptions,  the  latter  preparations  are  simply  mixt- 
ures of  cream  of  tartar  with  sodium  hydrogen  car- 
bonate, and  when  they  are  acted  upon  by  the  moist- 
ure of  dough,  the  following  reaction  takes  place : 

NaHCOs  +  KHC4H408  =  KNaC^Oe  +  COa  +  HaO. 

The  carbonic-acid  bubbles,  escaping,  render  the 
bread  or  cakes  light ;  the  double  tartrate,  Rochelle 
salt,  remains  behind.* 

Several  other  tartrates  are  used  in  medicine, 
and  one  of  them,  tartar  emetic,  is  particularly  im- 
portant. It  is  a  double  salt  containing  potassium 
and  antimony,  and  is  commonly  represented  as  con- 
taining the  latter  metal  so  united  with  oxygen  as 
to  form  a  univalent  radicle  —  Sbm  =  O.  Upon  this 

TC     ) 
basis,  tartar  emetic  would  be  written,  CUQ  [  C4H4O6 ; 

but  recent  investigations  show  that  its  constitution 
is  more  complicated.  The  salt  is  a  powerful  emetic, 
and  in  large  doses  is  poisonous. 

One  other  fruit-acid,  although  not  derived  from 
the  foregoing  acids,  may  fairly  be  described  here. 
Citric  acid,  C6H8O7,  is  found  in  oranges  and  lemons, 
and,  with  malic  acid,  in  such  fruits  as  the  currant 
and  gooseberry.  It  forms  white,  soluble  crystals, 
which  contain  three  COOH  groups,  and  therefore 
three  atoms  of  replaceable  hydrogen.  Hence  it 
can  form  various  salts,  thus : 

(H  (K  (K  (K 

C6H607  \  H          C6H607  \  H          C6H507  \  K        C6H6O7  \  K 

(H  (H  (H  (K 

Citric  acid.  Monopotassic  citrate.      Dipotassic  citrate.      Tripotassic  citrate. 

Etc. 

*  Mrs.  Richards's  little  book  on  "  The  Chemistry  of  Cooking  and 
Cleaning  "  may  be  profitably  read  in  connection  with  this  and  the  fol- 
lowing chapter. 


CHAPTER  XXXVII. 

GLYCERIN  AND   THE   FATS. 

IN  preceding-  chapters  we  have  become  acquaint- 
ed with  two  classes  of  alcohols,  derived  from  univ- 
alent  and  bivalent  hydrocarbon  radicles  respect- 
ively. These  alcohols,  we  have  seen,  are  simply 
hydroxides,  which,  though  very  different  in  their 
outward  properties,  may  be  compared  as  to  struct- 
ure with  the  hydroxides  of  the  metals.  Still  other 
series  of  alcohols  are  known,  some  of  which  cor- 
respond to  radicles  of  higher  valency  ;  and  these 
we  may  compare  with  inorganic  hydroxides,  thus : 

I.  II.  III.  IV. 

KOH.  Ca(OH)3.  Bi(OH),.  Si(OH)«. 

CHsOH.          C2H4(OH)2.        C8H6(OH)3.        C4H6(OH)4. 

There  is  also  an  alcohol,  mannite,  which  is  de- 
rived from  a  sexivalent  radicle.  Its  formula  is 
C6H8(OH)6 ;  but  its  description,  as  well  as  that  of 
the  compound  cited  in  the  fourth  column  above, 
erythrite,  must  be  looked  for  in  some  of  the  larger 
treatises  upon  organic  chemistry. 

The  trivalent  alcohol  C3H5(OH)3,  or  C3H8O3,  is, 
however,  a  body  of  great  practical  and  theoretical 
importance.  It  is  commonly  known  as  glycerin ; 


GLYCERIN  AND    THE  FATS. 

and  from  it  all  the  natural  fats  and  fatty  oils  are  sys- 
tematically derived. 

In  Chapter  XXXV  it  was  shown  that  when  a 
compound  ether  is  treated  with  caustic  alkalies  it  is 
decomposed,  an  alcohol  being  set  free  and  an  alka- 
line salt  formed.  For  example,  ethyl  acetate  and 
caustic  soda  yield  sodium  acetate  and  ethyl  alcohol, 
as  follows  : 

C2H6C3H3O2  +  NaOH  =  NaC2H3O2  +  C2H6OH. 

Now,  the  natural  fats  are  simply  ethers  correspond- 
ing to  glycerin,  and  they  may  be  decomposed  in 
precisely  the  same  way.  If  we  take  stearin,  which 
is  a  tristearate  of  glyceryl,  C3H5,  sodium  stearate 
will  be  formed  and  stearic  acid  will  be  liberated. 

C3H6(Ci8H36O2)3  +  sNaOH  =  C3H6(OH)3 


This  method  of  decomposition  is  known  as  saponifi- 
cation,  from  the  fact  that  the  alkaline  salts  produced 
by  it  are  ordinary  soaps. 

On  a  large  scale,  glycerin  is  prepared  either  by 
saponifying  a  fat  or  oil  with  lime  or  lead  oxide, 
which  yield  insoluble  calcium  or  lead  soaps  and  set 
the  glycerin  free,  or  else  by  acting  on  fats  under 
great  pressures  with  superheated  steam.  The  latter 
process  readily  decomposes  a  fat,  and  separates  it 
at  once  into  glycerin  and  an  acid  in  such  a  way  that 
both  products  are  immediately  recoverable.  In  the 
preparation  of  stearic  acid  this  method  of  decompo- 
sition is  practically  applied,  and  both  glycerin  and 
the  acid  are  saved.  The  latter  is  used  in  the  manu- 
facture of  candles.* 

*  For  details  about  the  stearine  industry,  see  Wagner's  "  Chemical 
Technology,"  pp.  620-636. 


3i8  ORGANIC  CHEMISTRY. 

Glycerin  is  a  colorless,  sirupy  liquid,  of  specific 
gravity  1.28.  It  solidifies  at  low  temperatures,  and 
distills,  with  partial  decomposition,  at  275°-28o°.  It 
distills  more  perfectly  in  a  vacuum.  It  has  a  very 
sweet  taste,  and  mixes  readily  in  all  proportions  with 
water  and  alcohol.  It  has  a  great  variety  of  uses,  as 
a  solvent  or  as  a  lubricator,  and  its  household  appli- 
cation to  chapped  lips  or  hands  is  universally  famil- 
iar. With  feeble  oxidizing  agents  it  yields  gly eerie 
acid,  C8H6O4. 

The  ethers  derived  from  glycerin  are  numerous, 
and,  at  first  sight,  complicated.  Since  the  alcohol 
itself  is  derived  from  a  trivalent  radicle,  and  has 
three  hydroxyl  groups,  it  follows  that  with  any 
given  monobasic  acid  it  may  form  at  least  three 
derivatives.  Thus,  with  acetic  acid,  HC2H3O2,  gly- 
cerin yields  three  ethers,  to  which  are  given  the 
names  that  are  written  below  the  subjoined  for- 
mulae: 

(  OH  (  C2HSO2 

C3H6  \  OH  C3HB  ]  OH 

(OH  (OH 

Glycerin.  Monacetin. 

(  CaH302  (  CaH303 

C3H6  \  C2H3Oa  C3H6  ]  C2H302 

(  OH  (  C2H3Oa 

Diacetin.  Triacetin. 

With  hydrochloric  acid  three  compounds  are 
obtained,  namely : 

(9  ( cl  ( cl 

-  C3H6 1  OH  C3H6  1  Cl  C3H6  ]  Cl 

(OH  (OH  (  Cl 

Chlorhydrin.  Dichlorhydrin.  Trichlorhydrin. 

In  fats  and  oils  we  generally  encounter  the  triple 
ethers  of  stearic,  margaric,  palmitic,  or  oleic  acids. 


GLYCERIN  AND    THE  FATS.  319 

Stearic,  margaric,  and  palmitic  acids  belong  to  the 
regular  fatty  series,  oleic  acid  stands  in  another 
group.  Stearic  acid  is  the  chief  acid  in  beef-suet, 
and  has  the  formula  QsHggOg ;  margaric  acid  is  one 
step  lower  in  the  series ;  and  palmitic  acid,  C16H32O2, 
is  derived  both  from  animal  fats  and  from  palm-oil. 
Oleic  acid,  QsH^O^  is  found  in  olive-oil  and  in  sev- 
eral other  fatty  substances.  All  these  fats  and  oils 
may  be  represented  by  the  subjoined  formulae : 

(  C16HS102  (  C17H,3Oa 

C3H6  \  C16H3iOa  C3H8  \  C17H33Oa 

(  Ci8H81Oa  (  Ci7H33Oa 

Tripalmitin.  Trimargarin. 

C18H3502  (  C18H33Oa 

Ci8H36Oa  CsHs  -s  CisH33Oa 

C18H35Oa  (  C18H33Oa 

Tristearin.  Triolein. 

They  are  commonly  called  by  the  briefer  names  of 
palmitin,  margarin,  stearin,  and  olein,  respectively. 
The  more  stearin  a  natural  fat  contains,  the  more 
solid  it  is  ;  the  fluid  or  pasty  fats  are  richer  in  olein. 
Other  glycerin  ethers  are  often  found,  but  they  need 
no  full  description  here. 

Soap  is  a  mixture  of  the  alkaline  salts  of  the  fore- 
going acids,  and  is  prepared  by  the  direct  action 
of  caustic  soda  or  potash  upon  fats.  A  soap  which 
contains  mostly  soda  salts  and  little  of  the  oleate  is 
a  hard  soap  ;  potash  soaps,  or  soaps  containing  much 
oleic  acid,  are  soft  soaps.  Sometimes,  in  making 
cheap  soaps,  rosin  is  added ;  and  in  some  cases,  a 
solution  of  sodium  silicate,  or  water-glass,  is  also 
used.  A  pure  soap  is  completely  soluble  in  alcohol. 
All  soaps  contain  a  considerable  quantity  of  water. 

When  glycerin  is  treated  with  a  mixture  of  strong 


320 


ORGANIC  CHEMISTRY, 


nitric  and  sulphuric  acids,  an  ether  is  formed  which 
is  commonly  known  as  nitroglycerin.  This  trini- 
trin,  as  it  is  more  properly  named,  is  a  yellow,  oily 
liquid  having  the  formula  C3H5(NO3)3,  and  possesses 
extraordinary  explosive  properties.  When  kindled 
by  a  flame,  it  burns  rather  quietly  ;  but  when  struck 
by  a  hammer,  or  ignited  by  a  percussion-cap,  it  ex- 
plodes with  terrific  violence.  This  explosion  is  sim- 
ply a  sudden  decomposition,  one  effect  of  which  is 
to  develop  instantaneously  a  very  large  volume. of 
gas,  in  accordance  with  the  following  equation : 

4C3H6N3O9  =  I2CO2  +  I2N  +  20  +  ioH20. 

Dynamite  and  several  other  explosive  agents  much 
used  in  blasting  are  mixtures  of  nitroglycerin  with 
silica,  fine  sand,  sawdust,  or  some  other  solid  pow- 
der. The  oil  itself  is  also  used  directly  as  an  ex- 
plosive. Nitroglycerin  is  a  substance  which  should 
only  be  handled  with  extreme  care,  for  it  is  not 
merely  explosive  but  also  very  poisonous.  A  sin- 
gle drop  placed  on  the  tongue  will  produce  intense 
headache ;  and  similar  discomfort  may  arise  from 
mere  contact  of  the  liquid  with  the  fingers. 

When  glycerin  or  any  fat  is  heated  to  the  point 
at  which  decomposition  begins,  acrid  vapors  are 
given  off.  These  are  produced  by  a  substance  called 
acrolein,  the  odor  of  which  may  be  recognized  in  the 
unpleasant  fumes  emitted  from  the  wick  of  an  imper- 
fectly quenched  candle.  Its  formula  is  C8H4O,  and 
it  is  the  aldehyde  corresponding  to  allyl  alcohol  and 
acrylic  acid.  These  three  compounds  are  related  to 
each  other  in  the  same  way  as  are  common  alcohol, 
aldehyde,  and  acetic  acid,  as  the  subjoined  formulae 
will  show : 


GLYCERIN  AND    THE  FATS.  321 

Ethyl  alcohol,  CaH6O.     Aldehyde,  C2H4O.    Acetic  acid,  C2H4Oa. 
Allyl       "        C3H«O.     Acrolein,     C3H4O.    Acrylic  "      C3H4O2. 

Allyl  alcohol,  C3H5,  OH,  is  interesting  in  several 
ways.  It  is  the  hydroxide  of  a  univalent  radicle, 
C3H5,  which  is  isomeric  with  the  trivalent  radicle 
of  glycerin.  These  two  radicles  differ  in  structure, 
however,  as  the  following  formulae  for  the  alcohols 
indicate : 

CH2OH  CH3 

CHOH  CH 

CH2OH.  CHaOH. 

Glycerin.  Allyl  alcohol. 

A  good  many  derivatives  of  allyl  are  known, 
and  some  of  them  are  important.  Allyl  sulphide, 
(C3H5)2S,  is  the  natural  oil  to  which  garlic  owes  its 
odor ;  and  allyl  sulphocyanate,  C3H5,  CNS,  is  the  oil 
of  mustard.  The  radish,  horseradish,  etc.,  also  owe 
their  pungency  to  organic  compounds  of  sulphur. 


CHAPTER  XXXVIII. 

THE   CARBOHYDRATES. 

IN  sugar,  starch,  and  a  number  of  allied  com- 
pounds, the  hydrogen  and  oxygen  are  combined  in 
just  the  proportions  necessary  to  form  water.  By 
reagents  having  very  strong  affinity  for  water  this 
hydrogen  and  oxygen  may  be  removed,  and  char- 
coal is  left  behind.  For  instance,  strong  sulphuric 
acid  reacts  in  this  manner  upon  either  sugar  or 
starch,  as  the  pupil  may  easily  discover  by  experi- 
ment. Hence  the  term  carbohydrates,  or  hydrates  of 
carbon,  has  been  adopted  as  a  convenient  general 
name  for  this  class  of  substances,  notwithstanding 
the  fact  that  it  is  somewhat  misleading  as  to  their 
real  chemical  structure. 

A  considerable  number  of  carbohydrates  are 
known,  but,  as  some  of  them  are  isomeric  with 
others,  all  may  be  classed  in  three  groups  under 
three  simple  formulae.  These  groups  are  known  as 
the  sucroses,  or  sugars  proper ;  the  glucoses  ;  and  the 
amyloses,  or  starches  and  gums : 

Sucroses.  Glucoses.  Amyloses. 

CiaHaaOn.  C6H12O8.  C6H10O6. 

Cane-sugar.  Grape-sugar.  Starch. 

Milk-sugar.  Levulose.  Dextrin. 

Maltose.  Etc.  Gum. 

Etc.  Cellulose,  etc. 


THE  CARBOHYDRATES.  323 

Cane-sugar,  or  sucrose,  C^H^Ou,  is  found  in  the 
sap  of  many  plants,  such  as  the  sugar-cane,  sorghum, 
Indian  corn,  beet-root,  sugar-maple,  etc.  From  all 
these  sources,  and  perhaps  from  others,  it  may  be 
profitably  extracted ;  but  sugar-cane  is  the  most 
important.  Beet-root  sugar  is  extensively  made  in 
France,  and  maple-sugar  in  this  country ;  and  the 
manufacture  of  sugar  from  sorghum  is  an  industry 
which  promises  great  development  in  the  future.* 

In  the  extraction  of  sugar  from  sugar-cane  the 
latter  is  first  crushed  between  heavy  iron  rollers  so 
as  to  express  the  juice.  To  the  latter  a  little  lime  is 
immediately  added,  to  neutralize  certain  vegetable 
acids  and  to  precipitate  certain  fermentable  or  de- 
composable impurities.  The  liquid  is  next  heated 
to  boiling,  carefully  skimmed,  evaporated  in  copper 
pans  to  near  the  crystallizing  point,  and  filtered 
through  bags  of  cotton  or  linen.  On  cooling,  a  crys- 
talline mass  of  moist  brown  sugar  is  deposited ; 
and  the  remaining  syrup,  upon  further  evaporation, 
yields  still  more.  When  the  second  crop  of  crystals 
has  been  removed,  a  dark,  thick  molasses,  rich  in 
uncrystallized  sugar,  remains  behind.  This  is  either 
sent  into  market  as  it  is,  or  else  fermented  and  dis- 
tilled into  rum. 

Brown  sugar  owes  its  color  to  organic  impuri- 
ties, which  are  removed  by  the  following  process  of 
refining :  The  sugar,  dissolved  in  very  little  water, 
is  first  heated  in  a  copper  pan.  Albumen,  generally 
in  the  form  of  blood,  is  then  added,  which,  coagu- 
lating, carries  down  the  impurities  of  the  sugar  in  a 

*  The  United  States  Department  of  Agriculture  at  Washington  has 
issued  very  valuable  reports  upon  this  industry,  and  also  upon  the  sub- 
ject of  sugar  from  beets. 


324 


ORGANIC  CHEMISTRY. 


sort  of  dense  clot.  The  liquid  is  next  heated  to  the 
boiling-point  with  a  little  animal  charcoal,  and,  after 
running  through  a  charcoal  filter,  is  concentrated  to 
the  point  of  crystallization.  This  concentration  is 
now  generally  effected  in  a  vacuum-pan.  Finally, 
the  purified  sugar  is  drained  of  adhering  syrup  and 
dried. 

Pure  sugar  is  a  white,  crystalline  solid,  of  spe- 
cific gravity  1.59.  It  melts  at  160°,  forming  the 
amber-colored  mass  known  as  barley-candy.  At 
higher  temperatures  it  turns  brown,  loses  water, 
and  is  converted  into  a  substance  called  caramel, 
which  is  somewhat  used  for  coloring  alcoholic 
liquors.  In  rock-candy,  sugar  is  highly  crystal- 
lized ;  in  granulated  sugar  the  crystals  are  small 
and  separate ;  in  loaf  or  lump  sugar  the  crystalline 
character  is  evident  throughout  the  mass.  In  all 
of  these  forms  sugar  is  easily  soluble,  and  very 
sweet.  If  a  sample  of  commercial  sugar  fails  to 
dissolve  completely  in  hot  water,  the  insoluble  resi- 
due may  be  regarded  as  evidence  of  adulteration. 

Chemically  considered,  sugar  is  the  alcohol  of 
an  octad  radicle.  Its  eight  hydroxyl  groups  may 
be  replaced  by  eight  NO8  groups,  to  form  an  explo- 
sive octonitrate,  or  by  eight  acetic  groups  to  pro- 
duce an  octoacetate.  These  derivatives,  however, 
have  been  incompletely  studied. 

Lactose,  or  milk-sugar,  is  obtained  from  the 
whey  of  milk,  and  is  isomeric  with  sucrose.  It 
forms  hard,  white  crystals,  which  grit  between  the 
teeth,  and  are  less  sweet  than  cane-sugar.  They 
contain  one  molecule  of  water  of  crystallization,  so 
that  their  formula  is  written  C^H^On,  H2O.  Lac- 
tose is  used  in  preparing  the  little  globules  of  the 


THE  CARBOHYDRATES.  325 

homoeopathic  pharmacy.  Several  other  isomers  of 
sucrose  and  lactose  are  known. 

Cane-sugar  itself  does  not  undergo  fermenta- 
tion ;  but  by  the  action  of  yeast  it  is  converted  into 
a  mixture  of  two  glucoses,  both  of  which  ferment 
readily.  In  this  transformation  it  takes  up  one 
molecule  of  water,  so  that  the  whole  change  may  be 
written  out  as  follows  : 

CiaHaaOi,  +  H2O  =  C6H12O8  +  C8H12O«. 

One  of  these  glucoses  is  termed  dextrose  or  grape- 
sugar  ;  the  other  is  called  levulose  or  fruit-sugar. 
The  latter  is  the  more  readily  soluble  of  the  two, 
and  is  uncrystallizable.  Dextrose,  together  with 
sucrose,  occurs  in  many  fruits ;  with  levulose  it  is 
found  in  fruits  and  in  honey.  Commercial  glucose 
is  commonly  a  mixture  of  both  substances. 

On  a  large  scale,  glucose  is  made  by  the  action 
of  very  dilute  sulphuric  acid  upon  starch. 

EXPERIMENT  105. — Add  one  cubic  centimetre  of 
strong  sulphuric  acid  to  one  hundred  cubic  cen- 
timetres of  water,  and  heat  in  a  flask  to  boiling. 
Mix  ten  grammes  of  starch  to  a  thin  paste  with 
water,  and  pour  it  very  slowly  into  the  acid,  so 
as  not  to  check  the  boiling.  Continue  to  boil  for 
about  three  hours,  and  then  add  powdered  chalk 
until  all  free  acid  has  been  neutralized.  Filter  off 
the  insoluble  calcium  sulphate  thus  formed,  and 
evaporate  the  filtrate  to  the  consistency  of  a  thick 
syrup.  The  latter  will  be  sweet,  and  will  deposit 
crystals  of  dextrose  if  left  standing.  By  essentially 
this  process  immense  quantities  of  glucose  are  now 
made  from  the  starch  of  Indian  corn.  The  prod- 
uct is  cheaper  than  cane-sugar,  though  less  sweet, 


326 


ORGANIC  CHEMISTRY. 


and  is  largely  used  to  adulterate  sugars  and  syrups, 
in  the  manufacture  of  candies,  by  brewers  for  modi- 
fying the  quality  of  beer,  and  for  a  variety  of  other 
more  legitimate  purposes.* 

Starch,  which  has  the  formula  C6H10O5  or  some 
multiple  thereof,  is  found  in  all  grains,  in  such  vege- 
tables as  the  potato,  in  unripe  fruits,  and  to  a  greater 
or  less  extent  throughout  the  whole  plant-kingdom. 
Beans,  peas,  and  rice  are  especially  rich  in  it ;  sago 
and  tapioca  are  varieties  of  it ;  and,  in  short,  the 
nutritive  value  of  nearly  all  vegetables  depends  in 
great  part  upon  the  amount  of  starch  which  they 
contain.  Pure  starch  is  prepared  chiefly  from  wheat- 
flour  or  from  potatoes.  It  consists  of  a  white  pow- 
der made  up  of  microscopic  granules  (Fig.  53),  which 


FIG.  53. -Starch  Granules,  Magnified. 

are  insoluble  in  water.  If  heated  with  water  to 
above  60°,  however,  they  burst,  and  form  the  jelly- 
like  starch-paste  which  is  so  familiar  to  the  house- 
keeper. With  tincture  of  iodine  starch  forms  a  blue 
compound ;  and  by  this  reaction  it  may  be  distin- 
guished from  all  isomers.f 

*  The  question  whether  artificial  glucose  is  wholesome  or  not  is 
still  under  discussion.  At  the  worst,  it  is  not  a  dangerous  article  of 
diet. 

f  The  pupil  may  profitably  apply  this  test  for  starch  to  flour,  rice, 
bread,  potatoes,  etc.  Boil  each  article  with  a  little  water,  and  then 
add  a  drop  of  the  tincture. 


THE  CARBOHYDRATES. 


327 


By  heating  to  about  205°  starch  is  converted 
into  an  isomeric  compound,  dextrin.  This  sub- 
stance is  soluble  in  water,  yielding  a  gummy  solu- 
tion which  is  applied  to  the  backs  of  postage- 
stamps  and  used  for  other  similar  purposes.  Dex- 
trin is  largely  manufactured  under  the  name  of 
"  British  gum."  Most  of  the  natural  gums  are 
isomers  of  starch  and  dextrin.  Gum-arabic,  how- 
ever, is  a  mixture  of  the  potassium  and  calcium 
salts  of  arabic  acid,  (C6H10O5)2.  Pectin,  which  is 
found  in  most  fruits,  and  which  enables  their  juice 
to  form  jellies,  is  allied  to  the  gums  and  starches  ; 
but  its  exact  character  is  not  yet  definitely  under- 
stood. 

Cellulose,  (C6H10O5)3,  is  the  substance  which 
chiefly  constitutes  all  vegetable  fiber.  Wood  con- 
sists mainly  of  cellulose,  and  cotton  is  cellulose 
practically  pure.  By  sulphuric  acid  cellulose  may 
be  converted  into  glucose  ;  and  the  latter  may  be 
made  from  old  rags,  or  even  from  sawdust. 

When  cellulose  is  treated  with  a  mixture  of 
strong  nitric  and  sulphuric  acids  it  is  transformed 
into  nitrocellulose  or  pyroxylin.  This  compound, 
C6H7(NO2)3O5,  is  commonly  known  as  gun-cotton, 
and  is  remarkable  for  its  explosive  properties. 
Outwardly,  by  the  change  from  cotton  to  gun-cot- 
ton, the  vegetable  fiber  remains  the  same ;  and  it 
may  be  spun  into  thread,  woven  into  cloth,  or  made 
into  paper,  the  same  as  before.  It  explodes,  how- 
ever, either  by  percussion  or  upon  the  touch  of  a 
flame,  more  violently  than  gunpowder;  and  it  is 
somewhat  used  as  an  explosive  agent. 

Gun-cotton  dissolves  easily  in  a  mixture  of  al- 
cohol and  ether,  forming  a  solution  which  is  known 
15 


328  ORGANIC  CHEMISTRY. 

as  collodion.  This  liquid  evaporates  rapidly,  leav- 
ing- a  film  of  gun-cotton  behind ;  and  it  is  used  for 
a  variety  of  surgical  purposes  and  for  photography. 
The  latter  use  was  described  in  a  previous  chapter ; 
its  surgical  value  is  due  to  its  power  of  covering 
raw  or  inflamed  surfaces,  as  in  the  case  of  scalds 
and  burns,  with  a  sort  of  artificial  skin,  and  thereby 
protecting  them  from  contact  with  the  air.* 

*  Details  concerning  many  of  the  bodies  described  in  this  chapter 
may  be  read  up  to  advantage  in  Wagner's  "  Chemical  Technology." 


CHAPTER  XXXIX. 

THE   BENZENE   DERIVATIVES. 

BENZENE,*  C6H6,  is  a  hydrocarbon  of  remark- 
able interest.  It  has  been  prepared  by  synthesis 
from  acetylene,  C2H2,  and  by  several  other  meth- 
ods ;  but  it  is  chiefly  obtained  from  the  coal-tar 
which  accumulates  in  the  gas-works.  The  benzene 
is  purified  by  several  distillations,  and  forms  a  col- 
orless liquid,  lighter  than  water,  and  having  a  pe- 
culiar odor  resembling  coal-gas.  It  boils  at  80°,  and 
solidifies  at  3°.  Its  vapor,  as  well  as  the  liquid,  are 
highly  inflammable. 

Benzene  is  chiefly  useful  in  the  preparation  of 
its  derivatives ;  and  these  are  of  the  highest  impor- 
tance. They  are  all  derived  from  benzene  by  the 
substitution  of  other  elements  or  radicles  for  the 
hydrogen,  while  the  six  carbon-atoms  remain  as  a 
permanent  nucleus.  These  are  supposed  to  be  ar- 
ranged in  the  form  of  a  ring  or  closed  chain,  each 
having  three  bonds  of  affinity  satisfied.  Thus,  each 
carbon-atom  is  still  able  to  hold  one  hydrogen-atom, 
as  the  following  diagram  will  show  :  f 

*  Often  called  benz0/.  The  benzine  of  the  shops  is  usually  a  mixt- 
ure of  volatile  hydrocarbons  of  the  CnH2n  +  3  series.  It  is  obtained 
from  petroleum,  and  is  very  different  from  benzene  proper. 

f  Other  structural  formulae  are  possible,  but  this  one  is  the  best  for 
present  purposes. 


330  ORGANIC  CHEMISTRY. 

H 

i 

C 

H-C    XC-H 

ii       i 

H-C        C-H 


i 
H 

From  this  formula  the  formulas  of  the  derivatives 
are  easily  deduced,  as  a  few  examples  will  indicate  : 

H  H 

i  i 

/C\  C\ 

U-C      \-CH3  H-c'    %C-OH 

H-C        C-H  H-C        C-H 

\    #  \    / 

C  C 

I  I 

H  H 

Methyl-benzene,  C7H8.  Phenol,  C6H7O. 

H  H 

i  i 

C  C 

H-C      XC-NHa  H-C        C-COOH 

ii          i  ii          i 

H-C        C-H  H-C        C-H 

\    #  \    <f 

C  C 

H  H 

Aniline,  C6H7N.  Benzole  acid,  C7H0O2. 

Since  every  hydrogen-atom  in  benzene  is  thus  re- 
placeable, the  possible  number  of  benzene  deriva- 
tives is  almost  infinite.  Thousands  of  them  are 
actually  known  ;  hundreds  are  discovered  every 
year.  Only  a  few  of  the  more  striking-  and  useful 
can  be  described  in  this  treatise. 

Phenol,   C6H5OH,    commonly    called    carbolic 
acid,*  is  a  compound  of  great  value  as  an  antiseptic. 

*  It  is  not  really  an  acid. 


THE  BENZENE  DERIVATIVES. 


331 


It  is  chiefly  obtained  from  coal-tar  by  a  process  of 
distillation,  and  forms  white,  deliquescent  crystals 
which  melt  at  39.5°  and  boil  at  182°.  Commercial 
phenol  generally  has  a  reddish  tinge,  due  to  im- 
purities. It  has  a  smoky  odor  and  a  burning  taste, 
and  is  much  used  in  medicine  and  surgery  for  dis- 
infecting sick-rooms,  for  preventing  gangrene  in 
wounds,  etc.  It  is  highly  poisonous. 

By  the  action  of  strong  nitric  acid  upon  phenol 
the  latter  is  converted  into  trinitrophenol  or  pic- 
ric acid,  C6H2(NO2)3OH.  This  substance  occurs  in 
yellow,  intensely  bitter  crystals,  which  are  used  for 
giving  a  yellow  color  to  silk.  The  picrates  are 
salts  which  explode  violently  by  percussion,  and 
some  of  them  have  been  used  in  gunnery  and  in 
submarine  torpedoes. 

When  nitric  acid  acts  on  benzene  directly,  ni- 
trobenzene, C6H5NO2,  is  produced.  This  is  a 
volatile  liquid,  having  an  odor  like  that  of  bitter-al- 
monds. Although  somewhat  poisonous,  it  is  used 
in  the  manufacture  of  cheap  flavoring  essences 
and  in  perfumery.  Three  isomeric  dinitrobenzenes, 
C6H4(NO2)2,  all  solid,  are  also  known. 

When  nitrobenzene  is  mixed  with  iron-filings 
and  dilute  sulphuric  acid,  the  nascent  hydrogen 
evolved  from  the  two  latter  substances  reduces  it 
to  amidobenzene,*  or  aniline,  C6H5NH2.  This 
compound  is  sometimes  called  phenylamine,  the 
group  C6H5  being  frequently  known  as  phenyl. 
Aniline  is  an  oily  liquid  of  specific  gravity  1.036, 
which  boils  at  181°,  and  has  a  peculiar,  soapy,  dis- 

*  Compounds  containing  the  group  NH2  are  called  "amido-com- 
pounds."  Many  other  nitro-compounds  (containing  NOa)  are  similarly 
reducible  by  hydrogen. 


332  ORGANIC  CHEMISTRY. 

agreeable  odor.  It  is  a  powerful  base,  and  unites 
with  nearly  all  acids  to  form  highly  crystalline 
salts.  With  oxidizing  agents  it  yields  a  great  vari- 
ety of  derivatives ;  and  some  of  these  are  among 
our  most  valuable  and  brilliant  dyes.  Nearly  all 
the  gorgeous  colors  now  used  in  silks  and  satins  are 
prepared  indirectly  from  the  benzene  of  coal-tar. 
Some  of  them  are  salts  of  a  complex  base,  rosani- 
line,  CjjoHjgNg ;  which,  though  colorless  itself,  yields 
compounds  of  marvelous  beauty.  For  example, 
rosaniline  combines  with  hydrochloric  acid  to  form 
the  color  known  as  magenta.  This  substance,  in 
the  solid  state,  forms  crystals  of  a  rich,  metallic, 
beetle-green  color,  which  yield  with  alcohol  a  solu- 
tion of  a  magnificent  red.  Other  reds,  purples, 
violets,  yellows,  blues,  greens,  and  a  very  stable 
black  are  also  found  among  the  derivatives  of  ani- 
line. Thirty  years  ago,  coal-tar  was  worthless ;  to- 
day whole  industries,  giving  employment  to  thou- 
sands of  men,  depend  upon  it. 

In  some  of  the  preceding  chapters  we  have  stud- 
ied the  relations  of  certain  alcohols  to  derivatives 
known  as  acids  and  as  aldehydes.  In  all  aldehydes 
the  group  H— C=O  occurs,  and  in  all  acids  we 

find  the  more  complex  group  O  —  H  —  C=O.     In 

each  of  these  groups  one  carbon  bond  is  free,  by 
means  of  which  other  groups  can  be  chemically 
held  in  union ;  and  whenever  we  find  in  any  com- 
pound either  group,  that  compound  will  have  the 
properties  of  an  acid  or  an  aldehyde  as  the  case 
may  be.  Among  the  benzene  derivatives  we  meet 
many  compounds  illustrating  these  principles,  and 
a  few  formulae  will  make  the  subject  clear : 


THE  BENZENE  DERIVATIVES.  333 

H  H 

i  i 

C  C 

H-C    XC-COOH  H-C     XC-COH 

I!  I  II  I 

H-C        C-H  H-C        C-H 

\    s  \    s 

C  C 

H  H 

Benzoic  acid.  Benzaldehydc. 

H  H 

i  i 

C  C 

H-C      C-COOH  H-C    XC-COH 

H-C      C-OH  H-C      C-OH 

\     <f  \  ~  V 

C  C 

I  I 

H  H 

Salicylic  acid.  Salicyl  aldehyde. 

These  substances  are  of  some  importance.  Ben- 
zoic  acid  is  obtained  from  gum-benzoin,  and  is  of 
some  use  in  medicine  ;  benzaldehyde  is  the  well- 
known  fragrant  oil  of  bitter-almonds  ;  salicyl  alde- 
hyde is  the  odoriferous  principle  of  the  meadow- 
sweet spiraea ;  and  salicylic  acid,  which  is  now 
made  synthetically  from  phenol,  is  a  very  impor- 
tant remedy  in  the  treatment  of  rheumatic  disor- 
ders. Sodium  salicylate  is  often  used  instead  of 
the  acid.  Methyl  salicylate  is  the  natural  oil  of  the 
wintergreen  or  checkerberry. 

When  the  hydrogen  of  benzene  is  replaced 
by  a  radicle  of  the  methyl  series,  new  hydrocar- 
bons, homologous  with  benzene  itself,  are  pro- 
duced. Thus,  for  example,  we  have : 

Benzene,  CeHe. 

Methylbenzene,  C6H6CH3,    or  C7H8. 

Ethylbenzene,  C8H6CaH6,  "  C8H10. 

Propylbenzene,  C8H6C3H7,  "  C»Hi2. 


334  ORGANIC  CHEMISTRY. 

Dimethylbenzene,         C8H4(CH3)3,  or  C8Hi0. 

Trimethylbenzene,         C8H3(CH3)3,  "  C9H12. 

Tetramethylbenzene,    C6H2(CH3)4,  "  Ci0H14. 

etc. 

A  great  many  of  these  hydrocarbons  are  known, 
involving  interesting  cases  of  isomerism  ;  and  a  vast 
number  of  others  are  possible.  In  each  of  them  the 
unreplaced  hydrogen  of  the  original  benzene  is  still 
replaceable  by  other  atoms  and  radicles  as  before, 
while  the  hydrogen  of  the  methyl,  ethyl,  etc.,  groups 
is  also  capable  of  substitution.  Hence  the  deriva- 
tives of  these  compounds  are  very  complicated  in 
structure,  and  almost  innumerable.  The  possible 
benzene  derivatives,  containing  no  other  elements 
than  carbon,  hydrogen,  oxygen,  and  nitrogen,  would 
have  to  be  counted  by  millions. 

Next  to  benzene,  methyl  benzene  or  toluene, 
C6H5CH3,  is  the  most  important  hydrocarbon  of 
the  series.  With  nitric  acid  it  yields  nitrotoluene, 
C6H4NO2CH8,  which  is  easily  reduced  by  nascent 
hydrogen  to  amido-toluene,  C6H4NH2CH3,  a  com- 
pound which  is  more  commonly  known  as  toluidine. 
This  substance  occurs  to  some  extent  in  commercial 
aniline,  and  it  plays  an  essential  part  in  the  forma- 
tion of  the  aniline  dyes. 

We  have  already  noticed  that  benzene,  minus 
one  atom  of  hydrogen,  may  behave  like  a  univalent 
radicle,  and  that  this  group,  C6H5,  is  sometimes 
known  as  phenyl.  Now,  phenyl  may  replace  one 
hydrogen-atom  in  ethylene,  C2H4,  yielding  a  hy- 
drocarbon called  phenylethylene,  or  cinnamene, 
C2H3C6H5.  From  this  hydrocarbon  other  com- 
pounds may  be  in  turn  derived,  and  two  of  these 
are  noteworthy  : 


THE   BENZENE  DERIVATIVES.  335 

C  =  H3  C  =  Ha  C  =  HCOH  C  =  HCOOH 

C  =  Ha.          CHCeH6.  CHC6H6.  CHC6H6. 

Ethylene.  Cinnamene.          Cinnamic  aldehyde.  Cinnamic  acid. 

Cinnamic  aldehyde,  C9H8O,  is  the  chief  constituent 
of  the  fragrant  oil  of  cinnamon  ;  and  from  cinnam- 
ic  acid,  by  a  series  of  synthetic  processes,  indigo 
has  been  obtained.  Indigo  originally  was  prepared 
from  the  leaves  and  stems  of  the  indigo-plant,  which, 
covered  with  water  and  allowed  to  ferment,  gradu- 
ally yielded  this  valuable  coloring-matter.  When 
absolutely  pure  its  formula  is  C16H10N2O2  ;  and  it  is 
probable  that  in  the  near  future  it  will  be  largely 
made  artificially  from  among  the  hydrocarbon  prod- 
ucts of  coal-tar.*  Even  at  the  date  of  writing,  arti- 
ficial indigo  is  being  produced  in  Germany  upon  a 
commercial  scale. 

In  addition  to  the  great  number  of  hydrocar- 
bons derivable  from  benzene  by  the  substitution  of 
hydrogen,  still  others,  even  more  complicated,  are 
formed  by  the  combination  of  two  or  more  benzene 
rings  with  each  other.  A  few  formulae  will  illus- 
trate this  matter  : 


H    H          H    H 

i       i  i       i  C        C 

C-C  C-C  x    \    /  \ 

^         %        #        \  TT  _  r*       r*       r*    TJ 

H-C  C-C  C-H  7       7        T~ 

v  /    v  r  H~c   c    C-H 

C  =  C  C  =  C  \    /    \  s 

i       i  i      i  C        C 

H     H  H     H  i          i 

Diphenyl,  C18H10.  H          H 

Naphthalene,  C10H8. 

*  Full  details  concerning  the  synthesis  of  indigo  would  be  too  com- 
plicated for  introduction  in  a  school  text-book.  For  such  matters  the 
larger  treatises  upon  organic  chemistry  may  be  consulted.  Strecker's 
treatise  is  good. 


336  ORGANIC  CHEMISTRY. 

H  H 

i  i 

C         H         C 

H-C       C-C-C         C-H 

H-C        C-C-C         C-H 

\    x       i        \    s 

C         H         C 

H  H 

Anthracene,  Cj4H10. 

From  all  such  hydrocarbons  as  these  a  vast  num- 
ber of  complicated  derivatives  may  be  obtained,  and 
some  of  them  have  great  practical  importance. 
Naphthalene  and  anthracene  are  both  white  solids, 
obtained  from  coal-tar  oil,  and  from  each  some  use- 
ful dye-stuffs  may  be  prepared.  Thus,  from  naph- 
thalene we  get  naphthalene-yellow,  C10H5OH(NO2)2, 
and,  from  anthracene,  alizarin  and  purpurin  are 
artificially  obtained.  These  latter  substances  are 
found,  naturally,  in  the  madder-root,  which  has 
been  used  from  time  immemorial  as  a  red  dye,  and 
which  was  cultivated  over  large  areas  in  Eu- 
rope. The  familiar  Turkey-red  is  simply  the  color 
produced  by  madder.  Alizarin  has  the  formula 
C14H8O4,  and  purpurin  is  C14H8O5.  Both  com- 
pounds are  now  prepared  commercially  from  the 
anthracene  of  coal-tar,  and  the  land  upon  which 
madder  was  formerly  grown  is  now  released  to  the 
production  of  food.  By  the  single  discovery  of 
artificial  alizarin,  made  by  two  German  chemists  in 
1868,  hundreds  of  men  have  been  given  new  em- 
ployment, and  the  world's  wealth  has  been  percep- 
tibly increased. 

Enough  has  been  said  to  illustrate  the  general 
principles  which  govern  the  formation  of  the  de- 
rivatives of  benzene.  By  a  careful  study  of  the 


THE  BENZENE  DERIVATIVES.  337 

benzene  ring,  chemists  are  now  able  to  predict  the 
existence  of  compounds  in  advance  of  actual  dis- 
covery, and  to  plan  available  methods  for  their 
production.  Alizarin,  for  example,  was  thus  ob- 
tained— not  by  accident,  but  by  a  deliberate  applica- 
tion of  principles  with  skill  and  foresight.  Plainly, 
then,  the  consideration  of  the  structural  formulae, 
to  which  this  chapter  has  been  so  largely  devoted, 
is  not  by  any  means  a  useless  exercise  of  the  imagi- 
nation. The  formulas  may  be  capable  of  future 
improvement,  but,  as  they  now  stand,  they  are  of 
great  use  in  the  development  of  chemical  science. 


CHAPTER   XL. 

THE  TERPENES,   CAMPHORS,   ALKALOIDS,   AND 
GLUCOSIDES. 

THE  substances  described  in  this  chapter  are  all 
products  of  plant-life.  Some  of  them  are  struct- 
urally related  to  benzene,  but  for  the  greater  num- 
ber the  structure  is  as  yet  undetermined. 

The  terpenes  are  a  class  of  volatile  hydrocarbons 
of  the  general  formula  C10H16.  Most  of  them  occur 
as  the  so-called  "  essential  oils  "  of  plants ;  and,  al- 
though they  are  isomeric,  they  differ  widely  in 
their  external  properties.  The  oils  of  lemon,  or- 
ange, bergamot,  lavender,  pepper,  etc.,  are  exam- 
ples. There  are  many  others,  and  compounds  con- 
taining oxygen  are  often  mixed  with  them. 

In  common  turpentine,  which  exudes  from  cuts 
made  in  the  bark  of  several  species  of  pine,  we 
have  a  mixture  of  terpenes.  When  it  is  distilled 
with  water,  oil  of  turpentine,  C10H16,  distills  over, 
and  rosin  remains  in  the  retort.  The  oil  has  a  spe- 
cific gravity  of  0.86,  and  boils  at  161°.  The  rosin 
contains  oxygen,  and  consists  in  great  part  of  sylvic 
acid,  CgoHgoCV  In  structure  the  terpenes  are  un- 
doubtedly allied  to  the  benzene  series,  but  the 
causes  of  isomerism  remain  to  be  made  out.  That 
substances  so  different  as  turpentine,  oil  of  orange- 


THE  CAMPHORS  AND  ALKALOIDS.          339 

flowers,  and  oil  of  pepper,  should  have  the  same 
percentage  composition,  is  certainly  remarkable. 

The  camphors  are  closely  related  to  the  terpenes, 
but  contain  oxygen.  Ordinary  camphor,  which  is 
the  best  example,  is  a  white  solid,  having  the  for- 
mula C10H16O.  It  melts  at  175°,  boils  at  204°,  and 
has  a  peculiar,  characteristic  odor.  Nitric  acid  oxi- 
dizes it  to  camphoric  acid,  C10H16O4. 

In  a  great  many  plants,  especially  among  those 
which  possess  marked  poisonous  properties  or  me- 
dicinal value,  are  found  a  class  of  compounds  which 
are  termed  alkaloids.  Of  these  a  few,  containing 
only  carbon,  hydrogen,  and  nitrogen,  are  liquids ; 
the  others,  which  contain  oxygen  also,  are  crystal- 
lizable  solids.  They  are  all  bases,  and  unite  with 
acids  to  form  perfectly  definite,  well-characterized 
salts.  Only  a  few  of  them  can  be  noted  here. 

Of  the  liquid  alkaloids,  conine,  C8H15N,  and  nico- 
tine, Ci0H14N2,  are  the  most  noteworthy.  Conine  is 
the  active  principle  of  the  poison-hemlock  (Conium 
maculatum),  and  nicotine  is  contained  in  tobacco. 
Nicotine  is  an  oily  liquid,  of  a  disagreeable  odor, 
and  is  violently  poisonous.  Tobacco  contains  from 
two  to  eight  per  cent  of  it ;  but,  in  smoking,  the 
alkaloid  is  partly  decomposed. 

In  tea  and  coffee  we  find  a  remarkable  solid  al- 
kaloid, to  which  the  stimulating  effects  of  these 
articles  are  due.  This  alkaloid,  caffeine,  C8H10N4O2, 
crystallizes  in  silky  needles,  which  melt  at  178°  and 
sublime  at  higher  temperatures.  It  is  found  also 
in  the  leaves  of  the  Ilex  Paraguayensis,  or  Paraguay 
tea,  and  in  the  drug  known  as  guarana.  It  is  a 
curious  fact  that  widely  separated  nations  should 
select  as  stimulants  plants  which  belong  to  different 


340  ORGANIC  CHEMISTRY. 

genera  and  yet  depend  upon  the  same  alkaloid  for 
their  activity.  In  cocoa,  theobromine,  C7H8N4O2,  is 
found.  Caffeine  is  theobromine  with  one  hydrogen- 
atom  replaced  by  a  methyl  group. 

In  opium,  which  is  extracted  from  certain  spe- 
cies of  poppy,  at  least  fifteen  different  alkaloids  are 
found.  Some  of  these  occur  in  very  small  quantity 
and  are  unimportant,  but  the  following  are  note- 

worthy : 

Morphine,  CnH^NOs. 
Codeine,  Ci8HaiNO8. 
Thebaine,  Ci9HaiNO8. 
Narcotine,  Caa 


With  the  alkaloids  of  opium,  meconic  acid,  C7H4O7, 
is  combined.  All  of  these  alkaloids  are  useful  in 
medicine,  and  all  form  bitter  crystals  ;  all  are  poi- 
sonous, thebaine  being  the  most  so.  Morphine  is 
chiefly  used  as  sulphate,  and  is  invaluable  for 
quieting  pain.  Heated  under  pressure  with  hy- 
drochloric acid  it  yields  a  new  base,  apomorphine, 
C17H17NO2,  which  is  a  violent  emetic.  Codeine  is 
methyl-morphine,  C17H18(CH3)NO3. 

Cinchona,  or  Peruvian  bark,  is  another  drug  con- 
taining a  remarkable  group  of  alkaloids.  The  trees 
which  yield  it  grow  wild  in  the  mountainous  re- 
gions of  Peru  and  Ecuador,  and  are  extensively 
cultivated  in  Java  and  India.  Quinine,  C^H^NsC)^ 
and  cinchonine,  C^K^NgO,  are  the  most  important 
of  its  constituents.  Both  alkaloids  are  valuable 
remedies  in  the  treatment  of  fevers,  although  the 
first  named  far  surpasses  the  other.  It  is  intensely 
bitter,  and  is  administered  chiefly  as  sulphate. 

EXPERIMENT  106.  —  Dissolve  in  water,  with  the 
aid  of  a  drop  of  weak  sulphuric  acid,  a  little  quinine 


THE  ALKALOIDS. 


341 


sulphate.  The  solution  will  be  colorless  by  trans- 
mitted light,  but  with  a  reflected  ray  will  appear  of 
a  delicate,  misty  blue.  This  color  does  not  exist  in 
the  substance  itself,  but  is  produced  by  its  action 
upon  the  invisible  rays  of  the  spectrum  beyond  the 
violet.  The  property  of  producing  a  color  in  this 
peculiar  way  is  termed  fluorescence.  The  colorless 
assculin,  from  horse-chestnuts,  similarly  fluoresces 
with  a  brilliant  blue,  uranium  compounds  fluoresce 
with  a  greenish  yellow,  etc.  The  phenomenon  is 
beautiful,  and  not  uncommon.  •  • 

A  number  of  other  alkaloids  are  important,  but 
space  permits  only  the  barest  mention  of  them  here. 
In  the  nux  vomica  two  bases  exist — namely,  strych- 
nine, C^H^NjjOg,  and  brucine,  C^H^N^,  4H2O. 
Both  are  violent  poisons,  and  both  are  used  in  small 
doses  medicinally.  Aconitine,  from  aconite ;  atro- 
pine,  from  belladonna ;  hyoscyamine,  and  solanine, 
are  all  interesting.  Their  names  are  sometimes 
made  to  terminate  in  ia  instead  of  ine,  as  atropia, 
morphia,  quinia,  strychnia,  etc.  The  termination  is 
only  a  matter  of  preference. 

Although  the  chemical  structure  of  the  alkaloids 
has  not  yet  been  definitely  made  out,  chemists  are 
progressing  rapidly  toward  a  solution  of  the  prob- 
lem. Doubtless,  within  a  few  years,  most  of  these 
bases  will  be  prepared  by  synthesis.  At  present, 
the  following  points  seem  to  be  clear.  In  bone-oil, 
produced  by  the  distillation  of  bones,  a  series  of 
bases  are  found,  of  which  pyridine,  C5H5N,  is  the 
first  member.  By  the  destructive  distillation  of 
certain  alkaloids,  another  base,  chinoline,  is  formed  ; 
and  this  compound,  C9H7N,  is  closely  allied  to  pyri- 
dine, as  the  subjoined  formulae  will  show : 


342  ORGANIC  CHEMISTRY. 

H  ^       .  ?       V 

c  c      c 

H-^  Y  VH 

H-C        C-H  H-°x    X    ,C-H 

\    x  N        C 

N  i 

Pyridine.  H 

Chinoline. 

From  these  bases  and  their  allied  compounds  the 
alkaloids  are  in  all  probability  derived,  by  a  system 
of  hydrogen  substitutions  like  that  which  serves  to 
explain  the  derivatives  of  benzene.  The  similarity 
between  pyridine  and  benzene,  as  regards  structure, 
is  evident  at  a  glance  ;  while  chinoline  is  compara- 
ble with  naphthalene. 

Of  the  glucosides,  although  many  are  known,  but 
little  need  be  said.  These  compounds  exist  in  many 
plants  ;  and  by  the  action  of  certain  ferments  they 
are  decomposed  into  glucose  and  other  bodies 
which  are  in  general  derivatives  of  benzene.  The 
ferments  above  mentioned  are  complex  substances, 
of  which  the  exact  composition  remains  to  be  de- 
termined. The  manner  in  which  they  act  is  also 
little  understood.  The  following  glucosides  are  im- 
portant : 

Salicin,  C13H18O7,  is  found  in  the  bark  of  willows 
and  poplars.  It  forms  colorless,  bitter  crystals, 
which  are  easily  split  up  by  soluble  ferments  into 
glucose  and  saligenin,  C7H8O2. 

H2O  =  C7H8O2  +  CoH1206. 


Amygdalin,  CgoH^NOn,  is  the  crystallizable  bit- 
ter principle  of  bitter-almonds.  The  latter  also  con- 
tain a  ferment  called  emulsin,  and,  when  they  are 


THE  GLUCOSIDES.  343 

crushed,  the  latter  converts  the  amygdalin  into  ben- 
zaldehyde  (bitter-almond  oil),  hydrocyanic  acid,  and 
glucose. 

CaoHaTNOn  +  2H2O  =  C7H6O  +  HCN  +  2C6H12O6. 

The  oil  of  bitter-almonds  does  not  exist  in  the  per- 
fect fruit,  but  is  formed  entirely  by  this  reaction. 
In  the  equation  the  emulsin  does  not  appear. 

In  the  cambium  layer  of  coniferous  trees,  co- 
niferine,  C16H22O8,  is  found.  This,  with  a  ferment, 
yields  glucose,  and  coniferyl  alcohol,  C10H12O3. 
The  latter,  upon  oxidation,  is  converted  into  alde- 
hyde and  vanilline,  C8H8O8.  Vanilline  is  the  fra- 
grant principle  of  vanilla-beans,  although  it  may 
now  be  made  .artificially  from  the  coniferine  of  pine- 
trees.  Structurally,  it  is  a  derivative  of  benzene. 

Populin,  CaoH^Os,  from  the  aspen-tree  ;  fraxin, 
C27H30O17,  from  the  bark  of  the  ash  ;  phloridzin, 
C^H^OK,,  from  various  fruit-trees ;  and  assculin, 
C^H^O^,  from  the  horse-chestnut,  are  other  com- 
mon glucosides.  There  are  also  a  group  of  these 
compounds  derived  from  oak-bark,  nut-galls,  etc., 
which  are  known  as  the  tannic  acids  or  tannins. 
These  compounds  all  have  an  astringent  taste,  and 
yield  black  precipitates  with  salts  of  iron  ;  they  also 
act  upon  the  animal  membranes  (as,  for  example, 
the  skin)  forming  leather.  Probably  they  all  con- 
tain the  true  tannic  acid,  C14H10O9,  which  is  simply 
derived  from  gallic  acid,  C7H6OS,  a  derivative  of 

benzene  : 

C7HflO5  =  C6H2(OH)3COOH. 

Tannin  and  gallic  acid  are  both  used  in  the  manu- 
facture of  ink. 


CHAPTER  XLI. 

ANIMAL  CHEMISTRY. — FERMENTATION. 

WHEN  we  study  the  compounds  produced  by 
animal  life,  although  we  have  but  few  elements  to 
consider,  we  meet  with  compounds  of  the  very 
greatest  complexity.  As  a  rule,  subject  to  some 
exceptions,  they  contain  carbon,  hydrogen,  oxygen, 
and  nitrogen,  and  are  uncrystallizable.  Some  of 
them  contain  sulphur  or  phosphorus,  and,  except  in 
a  few  cases,  we  know  little  or  nothing  as  to  their 
chemical  structure. 

Two  groups  of  these  compounds  are  especially 
important,  inasmuch  as,  together  with  water,  fat, 
and  the  earthy  matter  of  the  bones,  they  make  up 
the  greater  part  of  every  higher  animal  organism. 
These  other  substances  we  have  already  considered, 
and  we  may  now  devote  our  attention  to  the  two 
groups  in  question,  the  albuminoids  and  the  gela- 
tins. 

The  albuminoids  are  a  class  of  substances  which 
are  best  represented  by  the  following  compounds. 
They  all  putrefy  easily,  coagulate  or  form  clots 
upon  heating  or  by  contact  with  alcohol,  and  are 
soluble  either  in  water  or  dilute  hydrochloric  acid. 

Albumen,  the  chief  compound  of  the  group,  is 
found,  dissolved  in  water,  in  the  whites  of  eggs  and 


ANIMAL   CHEMISTRY.— FERMENTATION.    345 

the  serum  of  blood.  The  change  from  fluid  to  solid 
white,  when  an  egg  is  boiled,  illustrates  the  coagu- 
lation by  heat  above  referred  to.  When  perfectly 
freed  from  water,  albumen  is  a  yellowish,  trans- 
parent solid,  having  a  composition  which  is  toler- 
ably well  represented  by  the  formula  C72H112N18SO22. 
A  similar  compound,  not  identical,  however,  is 
found  in  all  vegetable  juices.  It  is  called  vegetable 
albumen. 

EXPERIMENT  107.  —  Divide  the  white  of  an  egg 
into  three  portions,  and  put  them  into  three  different 
test-tubes.  Heat  one,  and  add  to  the  others  a  little 
alcohol  and  an  aqueous  solution  of  mercuric  chlo- 
ride respectively.  In  each  case  coagulation  will 
ensue.  Repeat  the  experiment,  if  convenient,  with 
a  little  blood.  One  drop  of  the  latter  in  each  test- 
tube  will  suffice. 

In  blood,  with  albumen,  are  found  two  other 
albuminoids,  which  so  react  upon  each  other  as  to 
form  a  third  substance,  called  fibrin.  The  latter 
separates  from  blood  very  soon  after  the  latter  has 
left  the  body,  and  forms  the  solid  clot.  The  al- 
bumen remains  behind  in  the  liquid  serum.  Fibrin 
is  best  obtained  by  heating  fresh  blood  until  a  clot 
is  produced,  and  washing  the  latter  thoroughly  un- 
der a  stream  of  water.  It  forms  a  mass  of  whitish 
or  grayish  fibers.  Blood  also  contains  a  crystalliza- 
ble  coloring-matter,  called  haemoglobin.  The  latter 
decomposes  easily  into  an  albuminoid,  and  a  body 
called  hematin,  which  contains  iron.  Its  probable 
formula  is  C^H^N^eO^ 

Casein,  the  albuminoid  constituent  of  milk  and 
cheese,  separates  in  curds  whenever,  milk  becomes 
sour.  With  it,  milk  contains  water,  fat  (or  butter), 


346  ORGANIC  CHEMISTRY. 

milk-sugar,  sodium  chloride,  calcium  phosphate,  etc. 
The  casein  is  held  in  solution  by  a  little  alkali,  and 
may  be  precipitated  by  acids.  Gluten  and  legumin 
are  vegetable  caseins. 

In  most  foods  the  albuminoids  play  an  important 
part.  When  they  are  taken  into  the  stomach  they 
first  dissolve  in  the  weak  hydrochloric  and  lactic 
acids  of  the  gastric  juice.  The  latter  fluid  also 
contains  a  peculiar  ferment,  called  pepsin,  which 
rapidly  converts  the  albuminoids  into  substances 
known  as  peptones,  and  these,  unlike  albumen  it- 
self, are  capable  of  diffusion  through  membranes. 
These  chemical  changes  are  essential  to  digestion, 
and  to  the  absorption  of  the  valuable  constituents 
of  the  food  into  the  system.  All  the  albuminoids 
dissolve  in  very  dilute  hydrochloric  acid  (one  part 
of  acid  in  a  thousand  of  water)  to  form  acid  albumen 
or  syntonin.  This  substance  does  not  coagulate 
upon  heating,  and  from  its  solution  alkalies  repre- 
cipitate  albumen. 

The  gelatins,  of  which  common  gelatin  is  the 
best  example,  are  obtained  from  bone,  cartilage, 
connective  tissue,  etc.  Common  gelatin  occurs  in 
commerce  in  sheets,  which  vary  in  color  according 
to  purity.  The  finest  qualities,  made  from  the 
"  sounds  "  of  certain  fishes,  are  used  for  making  jel- 
lies ;  the  coarser  grades  form  glue.  Gelatin  is  also 
valuable  in  various  photographic  processes,  in  mak- 
ing hektograph  plates,  and  for  many  other  purposes. 
It  dissolves  in  hot  water,  and  sets  to  a  jelly  on  cool- 
ing. By  tannin  it  is  precipitated  from  its  solutions, 
and  the  formation  of  leather  is  due  to  the  action  of 
the  tannin  of  the  tan-bark  upon  the  gelatinous  mat- 
ter of  skins.  Chondrin  is  a  peculiar  form  of  gelatin 


ANIMAL   CHEMISTRY.— FERMENTATION.  347 

obtained  from  rib  cartilage.  It  is  precipitated  from 
solution  by  nearly  all  acids,  whereas  ordinary  gela- 
tin is  not. 

As  might  be  naturally  inferred  from  their  great 
complexity,  the  albuminoids  and  gelatins  are  very 
unstable.  Their  unwieldy  molecules  tend  to  split 
up  into  simpler  groups  of  atoms ;  and  in  the  pro- 
cess of  putrefaction  they  are  the  compounds  which 
are  first  and  most  affected.  Putrefaction,  however, 
is  but  a  special  kind  of  fermentation ;  and  this  set 
of  phenomena  we  may  now  profitably  consider. 

Whenever  the  juice  of  fruits,  such  as  grapes  or 
apples,  is  freely  exposed  to  the  air,  a  series  of  changes 
occur  which  end  in  the  formation  of  alcohol.  If  the 
latter  be  left  to  itself,  a  further  change  takes  place, 
and  vinegar  is  produced.  Similar  reactions  are  no- 
ticed when  yeast  is  allowed  to  act  upon  starch  or 
sugar,  when  milk  turns  sour  or  butter  becomes  ran- 
cid, and  all  of  them  are  ascribed  to  fermentation. 
All  of  them  are  due  to  the  action  of  minute  living 
organisms,  microscopic  plants  or  animals,  and  of 
these  the  germs  are  found  nearly  everywhere.  The 
latter  may  be  killed  by  extreme  cold  or  extreme 
heat,  and  no  true  fermentation  can  occur  in  bodies 
from  which  they  are  excluded.  Milk,  fruit,  meats, 
vegetables,  fish,  etc.,  heated  to  boiling  and  sealed  up 
in  air-tight  tin  cans,  may  be  kept  for  years  without 
alteration ;  but,  when  they  are  exposed  to  air  con- 
taining ferment-germs,  fermentation  and  putrefac- 
tion speedily  ensue.  Antiseptics,  such  as  salt,  phe- 
nol, alcohol,  etc.,  owe  their  power  of  preventing 
decay  to  the  fact  that  they  kill  all  germs  of  fer- 
ments ;  and  ice  acts  as  a  preservative  by  chilling 
them  below  the  temperatures  at  which  they  are 


348 


ORGANIC  CHEMISTRY. 


capable  of  activity.  Many  contagious  diseases,  such 
as  small-pox,  typhoid  fever,  etc.,  are  also  ascribed  to 
similar  germs,  which,  when  inhaled,  set  up  processes 
of  fermentation  in  the  living  body  ;  and  disinfectants 
are  used  in  the  sick-room  for  the  direct  purpose  of 
destroying  these  dangerous  creatures.  Our  knowl- 
edge of  them  is  as  yet  in  its  infancy,  but  new  dis- 
coveries are  being  made  almost  daily  ;  and  we  may 
reasonably  hope  that  in  a  few  years  many  impor- 
tant advances  will  be  accomplished. 

In  putrefaction,  the  changes  which  the  albumi- 
noids undergo  are  so  complex  as  to  be  outside  the 
range  of  an  elementary  treatise.  The  following 
kinds  of  fermentation  are  simpler  : 

1.  Alcoholic  fermentation.     The  glucoses,  when 
exposed  to  the  action  of  the  yeast-plant,  undergo 
fermentation,  yielding  'large  quantities   of    carbon 
dioxide  and  alcohol.     Traces  of  succinic  acid  and 
glycerin  are  formed  at  the  same  time.     Sugar  and 
starch  have  first  to  be  transformed  into  glucoses  be- 
fore fermentation  can  take  place.     In  brewing,  the 
starch  of  the  grain  is  converted  into  glucose  by  a 
peculiar  substance  called  diastase,  which  is  formed 
in  the  process  of  malting.     Although  this  fermen- 
tation produces  alcohol,  an  excess  of  alcohol  will 
stop  it. 

2.  Acetous  fermentation.     This  produces  acetic 
acid,  and  is  noticed  when  wine,  cider,  beer-mash, 
etc.,  are  transformed  into  vinegar.     When  vinegar 
is  made  by  allowing  alcohol  to  trickle  over  wood- 
shavings,  the  latter  carry  the  ferment-germs  upon 
their  surfaces. 

3.  Lactic  fermentation.     This  occurs  when  milk 
turns  sour,  and  results  in  the  formation  of  lactic  acid. 


ANIMAL   CHEMISTRY.— FERMENTATION.  349 

4.  Butyric    fermentation.     This   yields   butyric 
acid,  and  is  observed  in  rancid  butter  and  putrefy- 
ing cheese. 

5.  Mucous   fermentation,  which  produces   gum 
and  mannite. 

6.  Nitric  fermentation,  recently  discovered,  by 
which  living  organisms  decompose  nitrates,  setting 
nitrogen  dioxide  free. 

For  a  full  discussion  of  the  subject  of  fermenta- 
tion, Schlitzenberger's  little  treatise  may  profitably 
be  consulted.* 

*  "  On  Fermentations."     No.  20  of  the   "  International  Scientific 
Series." 


V 


APPENDIX    I. 


COMPARATIVE   TABLE   OF   ENGLISH   AND 
METRIC   MEASURES. 


A.  Measures  of  Length. 

Standard  unit,  one  metre. 

i  kilometre     =  1,000  metres.  i  decimetre  =0.100  metre, 

hectometre  =     100      "  i  centimetre  =  o.oio      " 

decametre  =       10      "  i  millimetre  =  o.ooi      " 


metre          =  39.37079  inches, 
decimetre  =    3-93708       " 
centimetre  =    0.39371       " 
millimetre  =    0.03937       " 


i  inch  =2.53995    centimetres. 
I  foot  =  3.04794    decimetres, 
i  yard  =  0.914383  metre, 
i  mile  =  1.609315  kilometres. 


B.  Measures  of  Surface. 

i  sq.  metre  =  10.7643  sq.  feet.  i  sq.  foot  =  9.28997  sq.  dm. 
i  sq.  centimetre  =  0.1550  sq.  inch,  i  sq.  inch  =  6.45137  sq.  cm. 
I  sq.  millimetre  =  0.0015  sq.  inch,  i  sq.yard  =  0.8361  sq.  m. 

C.  Measures  of  Volume. 

I  litre  =  i        cubic  decimetre. 

i     "    =  1,000    "     centimetres. 

i  litre       =  61.02705  cu.  inches.      i  cu.  inch  =  16.38618  cu.  cm. 
i  cu.  cm.  =    0.06103  cu-  inch.          i  cu.  foot    =  28.31531  cu.  dm. 
I  litre       =    1.05672  U.  S.  qts.       I  U.  S.  qt.  =    0.9469    litre. 
16 


352  APPENDIX. 

D.  Measures  of  Weight. 

The  unit,  one  gramme,  is  the  weight  of  one 
cubic  centimetre  of  distilled  water,  at  the  tempera- 
ture of  4°  C. 

i  kilogramme     =i,ooogrs.  i  decigramme  =o.iooogr. 

i  hectogramme  =  100       "  i  centigramme  =  0.0100  " 

i  decagramme  =  10         "  i  milligramme  =  o.ooio  " 

i  kilogr.  =    2.204621  Ib.  avoir.  i  grain       =64.799    rnilligr. 

I      "      =32.15073    oz.  troy.  i  oz.  troy  =31. 1035  gr. 

I  gr.        =15.43235    grains.  I  Ib.  avoir.  =    0.45359  kilogr. 

One  thousand  kilogrammes  vary  but  little 
from  the  "  long  "  ton  of  2,240  pounds  avoirdupois 
(0.984206  ton). 

The  pound  avoirdupois  contains  7,000  grains. 

The  same  figures  which  represent  the  specific 
gravity  of  any  solid  or  liquid,  referred  to  water  as 
unity,  also  represent  the  weight  of  one  cubic  centi- 
metre of  the  substance,  expressed  in  grammes. 

THERMOMETRIC   RULES. 

To  reduce  a  Fahrenheit  temperature  to  its 
equivalent  in  centigrade  degrees :  Subtract  32°, 
and  multiply  the  remainder  by  -|. 

To  reduce  a  centigrade  temperature  to  its 
Fahrenheit  equivalent:  Multiply  by  f,  and  add  32° 
to  the  product. 


APPENDIX    II. 


QUESTIONS   AND   EXERCISES. 

To  be  amplified  or  increased  at  the  discretion  of  the  teacher. 

CHAPTER  I. — i.  How  do  chemical  and  physical  changes  differ? 
2.  Give  an  example  of  chemical  combination.  3.  Give  an  example  of 
chemical  decomposition.  4.  Give  some  points  of  connection  between 
heat  and  chemical  change.  5.  What  points  must  be  considered  in  the 
complete  study  of  a  chemical  change  ?  6.  What  is  understood  by 
matter?  What  by  force?  7.  Is  either  matter  or  force  destructible? 
8.  Define  chemistry.  9.  Name  some  useful  applications  of  chemistry. 

CHAPTER  II. — i.  Explain  what  is  meant  by  analysis  and  synthesis. 
2.  Define  elements  and  compounds.  3.  Which  of  the  following  sub- 
stances are  elements  ?  Iron,  oxygen,  water,  air,  copper,  wood,  salt, 
carbon,  sugar,  tin,  iodine.  4.  Explain  what  is  meant  by  a  molecule. 
5.  What  is  an  atom?  6.  What  is  a  mass  of  matter?  7.  From  what 
evidence  do  you  infer  the  existence  of  atoms  and  molecules  ? 

CHAPTER  III. — i.  Describe  three  methods  for  the  preparation  of 
hydrogen.  2.  How  does  hydrogen  occur  in  nature  ?  3.  Describe  the 
hydrogen-flame.  What  precaution  must  be  observed  in  kindling  it  ? 
4.  What  compound  is  formed  by  the  combustion  of  hydrogen?  5. 
What  substances  are  heavier  than  hydrogen?  What  does  one  litre 
of  hydrogen  weigh  ?  6.  What  law  governs  the  expansion  of  gases  by 
heat?  7.  How  does  the  volume  of  a  gas  vary  with  pressure?  8. 
What  pressure  and  what  temperature  are  taken  as  standards  of  com- 
parison ?  9.  Given  one  litre  of  gas  at  o°,  what  will  it  become  at  37°  ? 
What  at  83°  ?  What  at  273°  ?  10.  Seventy-two  volumes  of  hydrogen 
are  measured  at  16°,  what  will  they  measure  after  cooling  to  o°  ? 
What  at  —  273°  ?  ii.  Given  ten  litres  of  a  gas  at  22°  and  748  milli- 


354  APPENDIX. 

metres  pressure,  what  will  the  volume  be  at  o°  and  760  millimetres  ? 
12.  How  may  gases  be  liquefied  ?  13.  What  are  the  more  important 
properties  of  hydrogen?  14.  Is  hydrogen  a  metal  or  a  non-metal? 

CHAPTER  IV. — i.  How  does  oxygen  occur  in  nature  ?  2.  How  is 
oxygen  best  prepared  ?  What  precautions  are  essential  ?  3.  What  are 
the  chief  properties  of  oxygen?  4.  Define  oxidation.  What  is  an 
oxide  ?  5.  Is  oxygen  necessary  to  combustion  ?  6.  Is  oxygen  essen- 
tial to  respiration?  7.  Wherein  is  the  solubility  of  oxygen  in  water 
important?  8.  What  is  ozone?  Describe  its  properties.  9.  What 
does  a  litre  of  oxygen  weigh  ?  10.  \Vhat  volume  will  87  grammes  of 
oxygen  occupy  at  15°  and  774  millimetres  pressure  ?  n.  What  will  be 
the  weight  of  17  litres  of  oxygen,  measured  at  12°  and  755  millime- 
tres? 

CHAPTER  V. — i.  What  oxides  does  hydrogen  form?  2.  What 
happens  when  a  mixture  of  oxygen  and  hydro'gen  is  kindled  ?  3.  How 
much  heat  is  developed  by  the  combustion  of  hydrogen  ?  Does  any 
other  chemical  change  develop  more  heat  ?  4.  Explain  the  compound 
blow-pipe.  What  are  its  uses  ?  5.  Describe  the  electrolysis  of  water. 
6.  Describe  the  synthesis  of  water.  7.  In  what  proportions,  by  volume 
and  by  weight,  do  oxygen  and  hydrogen  combine  to  form  water?  8. 
Suppose  thirty-six  volumes  of  oxygen  and  hydrogen  unite,  what  vol- 
ume will  be  occupied  by  the  resulting  steam  ?  9.  What  weight  of 
oxygen  would  be  contained  in  one  gramme  of  liquid  water?  What 
volume  would  it  occupy  at  o°  and  760  millimetres?  10.  Given  ten 
litres  of  water  of  o°,  how  much  steam  will  it  give  at  100°  ?  What 
volume  of  hydrogen  can  be  obtained  from  that  steam?  What  weight 
of  hydrogen?  n.  What  are  the  chief  properties  of  water  ?  12.  How 
^does  water  behave  upon  solidifying  ?  13.  Define  a  gramme.  A  litre. 
A  kilogramme.  14.  Describe  the  centigrade  and  Fahrenheit  scales. 
15.  How  may  impure  water  be  purified  ?  16.  What  is  water  of  crystal- 
lization ?  Define  deliquescence  and  efflorescence. 

CHAPTER  VI. — i.  How  does  nitrogen  occur  in  nature?  2.  How 
may  nitrogen  be  prepared  ?  3.  What  is  the  composition  of  the  atmos- 
phere ?  Does  it  vary  in  any  way  ?  4.  Describe  the  chief  properties 
of  nitrogen.  5.  What  is  the  weight  of  one  litre  of  nitrogen,  at  o°  and 
760  millimetres  ?  6.  What  is  the  weight  of  7.33  litres  of  air,  measured 
at  22°  and  758  millimetres  ? 

CHAPTER  VII. — i.  Describe  ammonia  gas.  What  is  its  exact  com- 
position? 2.  What  is  aqua  ammonia?  3.  Name  the  oxides  of  nitro- 
gen. 4.  Describe  nitric  acid.  What  is  a  nitrate?  5.  What  action 
has  nitric  acids  on  metals  ?  6.  Define  "  acid  "  and  "  alkali."  7.  What 
are  salts  and  bases?  8.  Explain  the  names  nitrous  and  nitric.  9. 


QUESTIONS  AND  EXERCISES.  355 

Give  the  law  of  definite  proportions.  10.  Give  the  law  of  multiple 
proportions.  Illustrate  it.  n.  Describe  nitrous  oxide  and  its  uses. 
12.  Describe  nitrogen  dioxide  and  nitrogen  tetroxide. 

CHAPTER  VIII. — I.  What  is  a  chemical  symbol  ?  Give  examples. 
2.  Explain  the  combining  weights  of  oxygen  and  nitrogen.  3.  Ex- 
plain the  combining  weights  of  Cl,  Br,  I,  K,  Na,  and  Ag.  4.  State  the 
atomic  theory,  and  explain  what  is  meant  by  atomic  weight.  5.  Give 
and  explain  the  formulae  of  several  compounds.  6.  What  weight  of 
oxygen  can  be  prepared  from  sixty  grammes  of  KClOs  ?  What  vol- 
ume, measured  at  10°  and  740  millimetres  ?  7.  Explain  this  equa- 
tion :  Fe  +  H2SO4  =  H2  +  FeSO4.  What  weights  of  iron  and  of  sulphu- 
ric acid  would  be  needed  to  give  fifty  grammes  of  hydrogen  ?  8.  Sixty- 
five  litres  of  oxygen  are  wanted,  at  27°  and  750  millimetres  ;  what  weight 
of  KC1O3  must  be  used  ? 

CHAPTER  IX.— I.  Describe  the  different  forms  of  carbon.  2.  What 
are  the  uses  of  graphite  ?  3.  What  are  the  uses  of  amorphous  carbon  ? 

4.  How  does  charcoal  affect  coloring-matters  ?  How  does  it  act  as  a  dis- 
infectant ?     5.  What  is  coal  ?     6.  Describe  methane.     7.  What  is  ordi- 
nary coal-gas  ?     8.  Describe  a  gas-flame.     A  candle-flame.     9.  What 
is  a  Bunsen-burner  ?     10.  Describe  the  mouth  blow-pipe  and  its  uses. 
II.  Explain  the  safety-lamp. 

CHAPTER  X. — I.  Describe  carbon  monoxide.  2.  What  compound 
is  formed  when  charcoal  burns  ?  3.  How  do  you  test  for  carbon 
dioxide  ?  4.  How  is  COa  best  prepared  ?  5.  What  percentage  of 
COa  can  be  obtained  from  CaCO3  ?  6.  How  does  COa  affect  combus- 
tion and  respiration  ?  7.  Given  a  kilogramme  of  limestone,  what  volume 
of  COa  will  it  yield,  measured  at  21°  and  762  millimetres  ?  8.  How  is 
the  atmosphere  affected  by  plants  and  animals  ?  9.  What  is  cyanogen  ? 
10.  Define  a  compound  radicle.  II.  What  volume  of  oxygen  would  be 
required  for  the  complete  combustion  of  ten  grammes  of  charcoal  ? 
What  weight  of  COa  would  be  produced  ? 

CHAPTER  XI. — i.  How  is  the  density  of  carbon-vapor  determined  ? 
2.  State  the  two-volume  law.  3.  Why  should  the  formulae  CH  and  CN 
be  doubled?  4.  Why  should  the  formulae  N2O2  and  N2O4  be  halved? 

5.  What  is  the  vapor  density  of  C2H6O?  ofCeH6?  ofC6H7N?    6.  State 
Avogadro's  law.     7.  How  many  atoms  are  there  in  most  elementary 
molecules  ?     8.  Explain  the  formula  of  ozone. 

CHAPTER  XII. — i.  Define  valency.  2.  In  what  proportion  can  two 
monads  combine?  Two  dyads?  A  dyad  and  a  monad  ?  A  dyad  and 
a  triad  ?  A  dyad  and  a  tetrad  ?  3.  What  valency  has  the  metal  in 
each  of  the  following  formulae  ?  ZnBr2.  SbH3.  AuCl3.  CdO.  ThOa. 
TiCl4.  AlaO3.  WC16.  BaCO3.  Ag2CO3.  RbNO3.  Fe(NO3)2. 


356 


APPENDIX. 


4.  What  is  meant  by  a  structural  formula  ?  Give  examples.  5.  What 
is  an  unsaturated  compound  ?  6.  Explain  the  valency  of  cyanogen. 

CHAPTER  XIII. — I.  What  elements  form  the  chlorine  group?  How 
are  they  related  ?  What  are  their  atomic  weights  ?  2.  Describe  hy- 
drofluoric acid.  3.  How  is  chlorine  best  prepared?  4.  What  are  the 
properties  and  uses  of  chlorine  ?  5.  How  does  chlorine  act  as  a  bleach- 
er or  disinfectant  ?  6.  How  is  hydrochloric  acid  prepared  ?  Describe 
it.  7.  What  weight.of  HC1  can  be  made  from  one  kilogramme  of  NaCl  ? 
How  much  HaSO4  would  be  used?  What  volume  would  the  HC1  oc- 
cupy at  17°  and  771  millimetres  ?  8.  What  action  has  hydrochloric 
acid  upon  metals  ?  What  salts  are  thereby  formed  ?  9.  Describe  aqua 
regia. 

CHAPTER  XIV. — I.  Write  the  formulas  of  the  oxides  and  acids  of 
chlorine.  Explain  their  names.  2.  What  hypochlorites  are  useful,  and 
why  ?  3.  What  are  the  properties  and  uses  of  the  chlorates  ?  4.  De- 
scribe bromine.  What  is  its  vapor  density?  5.  Describe  iodine.  6. 
What  is  a  convenient  test  for  iodine  ?  7.  Describe  the  chloride  and 
iodide  of  nitrogen. 

CHAPTER  XV. — I.  Point  out  the  similarities  between  O,  S,  Se,  and 
Te.  2.  Describe  sulphur.  What  is  the  character  of  its  molecule  ?  3. 
Describe  HaS.  What  volume  of  H2S  at  O°  and  760  millimetres  could 
be  evolved  from  50  grammes  of  FeS  ?  4.  What  weight  of  water  and 
of  SOa  would  be  formed  by  the  combination  of  one  litre  of  HaS.  5. 
Explain,  with  equations,  the  precipitation  of  some  metallic  salts  byH2S. 
6.  Which  is  the  most  important  oxide  of  sulphur  ?  What  are  its  prop- 
erties and  uses  ?  7.  Define  the  term  anhydride.  How  do  the  anhy- 
drides form  acids  ? 

CHAPTER  XVI. — I.  Give  the  names  and  formulae  of  the  sulphur 
acids.  2.  Explain  the  manufacture  of  H3SO4,  and  write  the  equations. 
3.  State  some  uses  of  sulphuric  acid.  What  is  its  action  upon  ordinary 
organic  matter?  4.  What  is  Nordhausen  acid?  5.  Define  a  dibasic 
acid.  6.  Explain  the  composition  of  the  lead  chamber  crystals.  7. 
What  is  hydroxyl  ?  8.  Write  structural  formulae  for  several  sulphur 
compounds.  9.  Describe  CSa. 

CHAPTER  XVII. — I.  Describe  the  preparation  and  properties  of 
ordinary  phosphorus.  2.  What  is  red  phosphorus  ?  3.  Describe  phos- 
phine.  4.  Explain  the  formulae  of  the  phosphoric  acids.  5.  How 
many  orthophosphates  of  sodium  are  possible?  6.  What  are  double 
and  triple  salts?  7.  What  is  the  valency  of  phosphorus?  8.  What 
volume  of  phosphorus-vapor  will  ten  grammes  of  the  solid  element 
yield  ? 

CHAPTER  XVIII. — I.  Point  out  the  similarities  between  P  and  As. 


QUESTIONS  AND  EXERCISES.  357 

2.  What  are  the  oxides  of  arsenic?    Which  one  is  the  more  useful,  and 
in  what  ways  ?     3.  How  does  boron  occur  in  nature  ?    Where  and  how 
are  its  useful  compounds  obtained  ?     4.  What  is  borax  ?     What  are  its 
uses?     5.  How  does  silicon  resemble  carbon?     6.  Describe  silicon  di- 
oxide.    7.  What  is  water-glass  ?  Crown  glass  ?  Bohemian  glass  ?  Flint 
glass  ?  Bottle  glass  ?  Porcelain  ?     8.  Describe  dialysis.     9.  Define  the 
terms  crystalloid  and  colloid. 

CHAPTER  XIX. — i.  How  do  metals  differ  from  non-metals?  2. 
What  is  electrolysis?  3.  Explain  the  galvanic  battery.  4.  What  is 
meant  by  electro-positive  and  electro-negative  elements  ?  Give  exam- 
ples. 5.  Which  of  the  following  pairs  of  elements  would  unite  vigor- 
ously, and  which  feebly  ?  O  and  Al.  S  and  N.  Pt  and  H.  F  and 
Ba.  Cl  and  K.  Br  and  Cl.  Si  and  Sb.  6.  Explain  the  electrolysis  of 
NaaSCu.  7.  How  do  neutral,  basic,  and  acid  salts  differ  in  constitu- 
tion ?  8.  Explain  Mendelejeff  s  classification  of  the  elements,  and  his 
prediction  of  the  existence  of  undiscovered  metals. 

CHAPTER  XX. — I.  Name  and  compare  the  metals  of  the  alkalies. 
What  are  their  most  noteworthy  properties  ?  2.  Describe  caustic  soda. 

3.  What  weight  of  NaOH   can  be  prepared   from   84  grammes  of 
Na2CO3  ?    4.  Describe  the  Leblanc  soda  process.     What  great  indus- 
tries has   it  benefited  ?     5.  Name  the  chief  sources  of  potassium  com- 
pounds.    6.  What  is   saltpeter  ?    What  are    its  uses  ?    7.  Describe 
gunpowder.     8.  Explain  the  composition  of  the  ammonium  salts.     9. 
Explain  the  vapor  density  of  NH4C1. 

CHAPTER  XXI. — i.  How  does  silver  occur  in  nature  ?  2.  De- 
scribe an  amalgamation  process.  3.  Describe  the  Pattinson  process. 

4.  What  weight  of  AgNOs  can  be  made  from  125  grammes  of  U.  S. 
coin  silver?     5.   How  is  silver  bullion  refined?     6.  State  and  illustrate 
Berthollet's  laws.     7.  Explain  photography.     8.  What  process  is  used 
in  plating  brass  with  silver  ? 

CHAPTER  XXII. — I.  How  do  Ca,  Sr,  and  Ba  chiefly  differ  ?  2. 
Describe  CaO  and  Ca(OH)2.  What  are  their  chief  uses?  3.  De- 
scribe CaCO3.  4.  Describe  gypsum  and  plaster.  5.  What  is  "hard" 
water?  What  is  its  action  in  the  steam-boiler,  and  in  the  laundry. 
6.  What  uses  have  the  compounds  of  Sr?  7.  Explain  a  regen- 
erative process  for  making  oxygen.  8.  What  are  the  properties  of 
BaSO4  ? 

CHAPTER  XXIII.— i.  How  is  white  light  affected  by  a  prism? 
2.  How  is  colored  light  affected  by  a  prism  ?  3.  How  may  sodium  or 
barium  be  detected  by  the  aid  of  a  prism  ?  4.  Describe  a  common 
spectroscope.  5.  Describe  a  direct-vision  spectroscope.  6.  What  ele- 
ments are  conveniently  detected  with  the  spectroscope  ?  7.  What  ele- 


358  APPENDIX. 

ments  have  Been  discovered  with  the  spectroscope  ?  8.  What  is  an 
absorption  spectrum  ?  9.  How  does  the  light  emitted  by  hot  gases 
differ  from  that  emitted  by  solids  ?  What  sort  of  a  spectrum  would 
a  candle-flame  give?  10.  Describe  and  explain  the  solar  spectrum. 
ii.  Describe  the  reversal  of  the  sodium-line.  12.  Wrhat  do  you  know 
of  the  spectra  of  stars  and  nebulae? 

CHAPTER  XXIV. — i.  What  important  gems  contain  glucinum  ? 
2.  Give  the  valency  and  atomic  weight  of  magnesium,  zinc,  cadmium, 
and  mercury.  Illustrate  the  valency  by  some  formulae.  3.  How  does 
magnesium  occur  in  nature  ?  What  are  its  properties  ?  4.  Describe 
magnesium  sulphate.  What  is  meant  by  water  of  constitution  ?  5. 
How  is  zinc  extracted  from  its  ores  ?  What  are  its  properties  ?  6. 
Describe  ZnO,  ZnSO4,  and  ZnS.  7.  What  is  meant  by  Burnettized 
timber  ?  8.  What  are  the  properties  and  uses  of  cadmium  ?  9.  Ex- 
plain the  vapor  density  of  cadmium  and  mercury.  10.  Where  and 
how  is  mercury  obtained  ?  11.  Describe  metallic  mercury.  What 
classes  of  compounds  does  it  form  ?  12.  Describe  HgO,  HgCl,  HgCl2, 
and  Hgla. 

CHAPTER  XXV. — i.  Describe  aluminum  and  aluminum  bronze. 
State  the  atomic  weight  and  valency  of  aluminum.  2.  Describe  A12O3. 
What  is  a  sesquioxide  ?  3.  Describe  alum  and  its  uses.  What  other 
alums  are  possible  ?  How  do  they  resemble  each  other  ?  4.  What  are 
turquoise,  topaz,  cryolite,  and  lapis  lazuli?  What  is  ultramarine?  5. 
Give  a  brief  description  of  the  chemistry  of  pottery  and  porcelain.  6. 
Wherein  are  gallium  and  scandium  especially  interesting  ? 

CHAPTER  XXVI. — i.  Name  the  tetrad  metals  in  the  order  of  their 
atomic  weights.  2,  Describe  tin.  Where  and  how  is  it  found  in  na- 
ture ?  3.  What  is  tin-plate  ?  What  are  solder  and  bronze  ?  4.  De- 
scribe, with  formulae,  the  more  important  useful  compounds  of  tin.  5. 
What  ore  of  lead  is  most  important  ?  How  is  it  smelted  ?  6.  Describe 
metallic  lead.  7.  Are  lead  water-pipes  objectionable  ?  8.  What  oxides 
are  formed  by  lead  ?  9.  Describe  white-lead.  What  are  its  advantages 
and  disadvantages  compared  with  other  white  paints?  10.  In  what 
way  may  one  metal  precipitate  another  from  solution  ? 

CHAPTER  XXVII. — i.  Point  out  the  relations  connecting  N,  P,  V, 
As,  Sb,  and  Bi.  2.  Describe  antimony  and  its  uses.  3.  Explain  the 
differences  between  the  two  forms  of  SbaOa.  4.  Name  and  describe 
the  more  useful  antimony  compounds.  5.  Describe  bismuth  and  its 
uses.  6.  Describe  two  fusible  alloys  of  bismuth.  7.  Describe  the 
oxides  and  nitrates  of  bismuth. 

CHAPTER  XXVIII. — i.  How  do  chromous  and  chromic  compounds 
differ?  2.  Describe  CraO8  and  CrO3.  3.  Describe  the  useful  chro- 


QUESTIONS  AND  EXERCISES.  359 

mates.  4.  How  does  K3CraO7  behave  with  gelatin?  5.  Name  some 
uses  of  molybdenum  and  tungsten  compounds.  6.  State  the  law  of 
Dulong  and  Petit.  7.  Why  is  the  atomic  weight  of  uranium  put  at  239 
rather  than  at  119.5? 

CHAPTER  XXIX. — r.  What  oxides  are  formed  by  manganese? 
What  are  the  uses  of  the  commonest  one?  2.  Describe  MnSO*,  Mna 
(804)3,  and  KMnO4.  3.  How  is  iron  found  in  nature?  What  are  its 
chief  ores  ?  4.  How  do  wrought-iron,  cast-iron,  and  steel  differ  from 
each  other?  5.  How  is  wrought-iron  prepared?  6.  Describe  the 
blast-furnace.  7.  Describe  the  chief  methods  of  making  steel.  8.  How 
do  ferrous  and  ferric  compounds  differ?  9.  Describe  ferrou^sulphate. 
10.  Write  at  least  six  formulae  for  compounds  of  iron,  and  explain  the 
valency  of  the  metal. 

CHAPTER  XXX. — I.  What  are  the  sources  and  uses  of  nickel  ?  2. 
Write  formulae  to  illustrate  the  similarity  of  the  compounds  of  Fe, 
Ni,  and  Co.  3.  What' are  the  chief  uses  of  cobalt  compounds?  4. 
How  are  the  sulphide  ores  of  copper  smelted  ?  5.  Explain  the  Hunt 
and  Douglas  process.  6.  Name  the  leading  alloys  of  copper.  7.  De- 
scribe metallic  copper.  8.  Describe  the  electrotype  process.  9.  How 
may  copper  be  detected  in  solutions  containing  it  ?  10.  Give  an 
example  of  an  ammonio-metallic  base. 

CHAPTER  XXXI. — I.  How  does  gold  occur  in  nature?  How  is 
it  refined?  2.  Describe  the  process  of  quartation.  3.  What  are  the 
properties  of  gold  ?  4.  Write  formulae  illustrating  aurous  and  auric 
compounds.  5.  Describe  gold  trichloride  and  its  uses.  6.  Describe 
briefly,  in  general  terms,  the  metals  of  the  platinum  group.  7.  De- 
scribe platinum  and  its  uses.  What  is  platinum-black  ?  8.  WThat 
classes  of  compounds  are  formed  by  platinum  ? 

CHAPTER  XXXII. — I.  Define  organic  chemistry.  2.  Explain  the 
classification  of  the  hydrocarbons.  3.  What  is  an  homologous  series  ? 
4.  What  is  a  substitution  series  ?  5.  What  is  an  amine  ?  A  phos- 
phine?  6.  Illustrate  what  is  meant  by  isomerism.  7.  What  is  a 
polymeric  series  ? 

CHAPTER  XXXIII. — I.  Describe  cyanogen.  How  does  it  resem- 
ble chlorine  ?  2.  Describe  the  more  useful  double  cyanides  contain- 
ing iron.  3.  Describe  the  synthesis  of  carbamide.  4.  What  are  car- 
bonyl  and  sulphocarbonyl  ? 

CHAPTER  XXXIV.— I.  Explain  the  structure  of  the  methane 
series.  2.  Describe  petroleum.  3.  What  is  an  alcohol  ?  What  is  an 
ether?  4.  Describe  CH3OH.  5.  Describe  C2H6OH.  6.  What  is 
fractional  distillation?  7.  Describe  (C2H6)2O.  8.  What  is  a  mixed 
ether?  9.  Describe  chloroform  and  iodoform.  10.  Point  out  the 


360  APPENDIX. 

resemblance   in   chemical   structure  between  the  compounds  of  the 
univalent  hydrocarbon  radicles  and  the  compounds  of  potassium. 

CHAPTER  XXXV. — I.  What  is  an  aldehyde?  2.  How  are  the 
aldehydes  and  fatty  acids  derived  from  the  alcohols?  3.  What  group 
of  atoms  is  characteristic  of  organic  acids  ?  4.  Describe  acetic  acid. 

5.  Explain  the  isomerism  of  the  fatty  acids  and  their  ethers.     6.  What 
is  acetyl  ?     7.  What  is  an  amide  ?     8.  What  is  a  ketone  ? 

CHAPTER  XXXVI. — i.  Point  out  the  relations  between  paraffins, 
alcohol  radicles,  and  olefines.  2.  What  is  the  structure  of  C2H4  and 
some  of  its  derivatives  ?  3.  How  are  acids  derived  from  the  alcohols 
of  the  otefines?  4.  Describe  lactic  acid.  5.  Describe  oxalic  acid. 

6.  Write  formulae  for  succinic,  malic,  and  tartaric  acids.     7.  What  is 
baking-powder?     8.  Describe  citric  acid. 

CHAPTER  XXXVII. — I.  What  is  glycerin  ?  2.  Explain  the  struct- 
ure of  the  ethers  of  glycerin.  3.  What  are  stearin,  margarin,  palmitin, 
and  olein  ?  4.  What  is  a  soap  ?  5.  What  is  nitroglycerin  ?  6.  Point 
out  the  relations  between  allyl  alcohol,  acrolein,  and  acrylic  acid. 

CHAPTER  XXXVIII.— I.  What  are  the  carbohydrates?  How  are 
they  classified?  2.  Describe  sucrose.  3.  Describe  lactose.  4.  De- 
scribe glucose.  5.  What  is  starch  ?  Dextrin  ?  Gum-arabic  ?  6. 
What  is  cellulose  ?  7.  Describe  gun-cotton  and  collodion. 

CHAPTER  XXXIX. — i.  Explain  the  structure  of  benzene.  2.  De- 
scribe phenol.  3.  Describe  aniline.  4.  Illustrate  the  derivation  of 
acids  and  aldehydes  from  benzene.  5.  Illustrate  the  union  of  several 
benzene  rings  with  each  other.  6.  What  do  you  know  of  indigo,  alizarin, 
and  purpurin?  7.  What  are  the  uses  of  coal-tar? 

CHAPTER  XL. — i.  W7hat  is  a  terpene  ?  Give  examples.  2.  What 
are  the  alkaloids  ?  3.  Name  the  source  from  which  each  of  the  fol- 
lowing alkaloids  is  derived :  Strychnine,  caffeine,  quinine,  morphine, 
cinchonine,  and  nicotine.  4.  Compare  pyridin  and  chinolin  with 
benzene  and  naphthalene.  5.  What  is  a  glucoside  ?  6.  WThat  are  the 
useful  properties  of  tannin  ? 

CHAPTER  XLI. — i.  Describe  albumen.  2.  Describe  casein.  3.  How 
are  the  albuminoids  affected  by  the  gastric  juice  ?  4.  Describe  gelatin. 
5.  What  is  fermentation  ?  6.  How  do  disinfectants  check  the  spread 
of  disease  ?  7.  Name  the  different  kinds  of  fermentation. 


INDEX. 


Absorption  spectra,  218. 

Acetone,  309. 

Acetyl,  307. 

Acetyl  chloride,  308. 

Acetylene,  81. 

Acid,  60. 

acetic,  305. 

acrylic,  321. 

antimonic,  248. 

antimonious,  248. 

arabic,  327. 

arsenic,  162. 

arsenious,  161. 

benzoic,  333. 

boric,  164. 

bromic,  128. 

camphoric,  339. 

carbamic,  295. 

carbolic,  331. 

carbonic,  93. 

chloracetic,  308. 

chloric,  124. 

chlorous,  124. 

chromic,  254. 

cinnamic,  335. 

citric,  315. 

columbic,  252. 

cyanic,  294. 

cyanuric,  294. 

dithionic,  141. 

ethylsulphuric,  300. 

ferric,  270. 

gallic,  343. 

gly collie,  311. 

hydriodic,  130. 

hydrobromic,  128. 


Acid,  hydrochloric,  Ii8. 
hydrocyanic,  97,  291. 
hydroferrocyanic,  293. 
hydrofluoric,  112. 
hydrofluosilicic,  167. 
hydrosulphuric,  136. 
hypobromous,  128. 
hypochlorous,  123. 
hyponitric,  64. 
hypophosphorous,  155. 
hyposulphurous,  141. 
iodic,  130. 
lactic,  312. 
malic,  314. 
manganic,  263. 
margaric,  319. 
meconic,  340. 
metaphosphoric,  156. 
molybdic,  257. 
muriatic,  118. 
nitric,  58. 
nitrous,  61. 
oleic,  319. 
oxalic,  312. 
palmitic,  319. 
pentathionic,  141. 
perbromic,  128. 
perchloric,  127. 
periodic,  130. 
permanganic,  263. 
phosphoric,  155. 
phosphorous,  155. 
picric,  331. 
prussic,  97,  291. 
pyrophosphoric,  156. 
pyrosulphuric,  141,  147. 


362 


INDEX. 


Acid,  salicylic,  333. 

selenic,  149. 

selenious,  149. 

silicic,  170. 

stannic,  241. 

stearic,  319. 

succinic,  313. 

sulpliocarbonic,  295. 

sulphocyanic,  294. 

sulphuric,  142. 

sulphurous,  139. 

sylvic,  338. 

tannic,  343. 

tantalic,  252. 

tartaric,  314. 

telluric,  150. 

tellurous,  150. 

tetrathionic,  141. 

thiosulphuric,  141. 

trithionic,  141. 

tungstic,  257. 

vanadic,  247. 
Aconitine,  341. 
Acrolein,  320. 
yEsculin,  341,  343. 
Agate,  168. 
Air,  51,  53. 
Alabaster,  209. 
Albumen,  344. 
Albuminoids,  344. 
Alcohol,  allyl,  321. 

amyl,  300. 

butyl,  300. 

cetyl,  300. 

ethyl,  298. 

melissyl,  300. 

methyl,  298. 

propyl,  300. 
Aldehyde,  304. 

cinnamic,  335. 

salicylic,  333. 
Alizarin,  336. 
Alkali,  60,  184. 
Alkaloids,  339. 
Allotropy,  29. 
Alloys,  fusible,  250. 
Allyl,  alcohol,  321. 

sulphide,  321. 

sulphocyanide,  321. 
Alum,  234. 
Alumina,  233. 
Aluminum,  232. 


Aluminum,  bronze,  233. 

hydroxide,  233. 

sulphate,  234. 
Amalgam,  229. 
Amethyst,  168,  233. 
Amides,  308. 
Amidobenzene,  331. 
Amidotoluene,  334. 
Amines,  288. 
Ammonia,  55,  65,  193. 
Ammonium,  193. 

carbonate,  195. 

chloride,  56,  193. 

cyanate,  294. 

hydrosulphide,  194. 

hydroxide,  193. 

molybdate,  257. 

nitrate,  194. 

phosphate,  195. 

sulphate,  55,  194. 

sulphide,  194. 

sulphocyanate,  295. 

uranate,  258. 
Amygdalin,  342. 
Amyl,  acetate,  306. 

alcohol,  300. 

valerate,  306. 
Analysis,  8. 
Anhydrides,  140. 
Aniline,  331. 
Anthracene,  336. 
Anthracite,  79. 
Antichlor,  140. 
Antimony,  247. 

cinnabar,  250. 

chlorides,  248. 

hydride,  249. 

oxides,  248. 

sulphides,  248. 
Antozone,  31. 
Apatite,  151. 
Apomorphine,  340. 
Apple-oil,  306. 
Aqua  ammonia,  57,  193. 
Aqua  fortis,  59. 
Aquamarine,  222. 
Aqua  regia,  121. 
Arsenic,  159. 

compounds  of,  161,  162. 
Arseniuretted  hydrogen,  160. 
Arsenopyrite,  159. 
Arsines,  160,  289. 


INDEX. 


363 


Artiads,  157. 
Atmosphere,  53. 
Atom,  12. 
Atomic  heat,  259. 

theory,  69. 

weight,  66. 

weights,  table  of,  9. 
Atomicity,  105. 
Atropine,  341. 
Avogadro's  law,  103. 

Babbit's  metal,  248. 
Baking-powders,  94,  200,  312,  314. 
Barium,  205. 

compounds  of,  2 n,  212. 
Barytes,  211. 
Base,  61. 
Beeswax,  300. 
Belladonna,  341. 
Benzaldehyde,  332,  343. 
Benzene,  329. 
Berthollet's  laws,  200. 
Beryl,  222. 
Beryllium,  222. 
Bessemer  steel,  269. 
Bismuth,  250. 

compounds  of,  251,  252. 
Black-ash  process,  188. 
Black-lead,  76. 
Blanc-fixe,  211. 
Blast-furnace,  266. 
Bleaching,  117,  123,  138. 
Bleaching-powder,  123. 
Blende,  225. 
Blood,  345. 
Blooming,  265. 
Blow-pipe,  compound,  34. 

mouth,  86. 
Blue  vitriol,  277. 
Bone-black,  77. 
Borax,  165. 
Bornite,  275. 
Boron,  163. 

Boyle  and  Mariotte's  law,  22. 
Brass,  226. 
Brick,  236. 
Brimstone,  134. 
Britannia  metal,  241,  248. 
Bromine,  127. 
Bronze,  240. 
Brucine,  341. 
Brucite,  224. 


Brunswick-green,  162. 
Bunsen  burner,  86. 
Burnettizing,  227. 
Butane,  296. 
Butyl  alcohol,  300. 

Cadmium,  227. 

compounds  of,  228. 
Caesium,  184,  217. 
Caffeine,  339. 
Calamine,  225. 
Calcium,  205. 

carbonate,  207. 

chloride,  210. 

fluoride,  209. 

hydroxide,  206. 

hypochlorite,  123. 

oxide,  206. 

phosphate,  151,  209. 

sulphate,  208. 

sulphide,  188. 
Calomel,  230. 
Camphor,  339. 
Caramel,  324. 
Carbamide,  294. 
Carbohydrates,  322. 
Carbon,  74. 

dioxide,  91. 

monoxide,  90. 

sulphide,  149. 
Carbonado,  75. 
Carbonic  oxide,  90. 
Carbonyl,  295. 
Carburetted  hydrogen,  81. 
Carnelian,  168. 
Carre's  ice-machine,  58. 
Casein,  345. 
Cassiterite,  239. 
Cast-iron,  266. 
Catalysis,  26. 
Cellulose,  327. 
Cement,  207. 
Cerium,  237. 
Cetyl  alcohol,  300. 
Chalcedony,  168. 
Chalk,  206. 
Chalybite,  264. 
Chameleon  mineral,  264. 
Change,  chemical,  I. 

physical,  I. 
Charcoal,  76. 
Chemical  attraction,  6. 


INDEX. 


Chemical  calculations,  71. 

combination,  3. 

decomposition,  4. 

formulae,  70. 
Chemism,  6. 

Chemistry  defined,  6,  12. 
Chili  saltpeter,  189. 
Chinoline,  341. 
Chlorhydrins,  318. 
Chloride  of  lime,  123. 
Chlorine,  113. 

acids  of,  122. 

oxides,  122,  125. 
Chloroform,  302. 
Choke-damp,  95. 
Chondrin,  346. 
Chromates,  255. 
Chrome  alum,  254. 

orange,  257. 

red,  257. 

yellow,  256. 
Chromite,  253. 
Chromium,  253. 

compounds  of,  253,  254. 
Chrysoberyl,  222. 
Chrysolite,  169. 
Cinchonine,  340. 
Cinnabar,  228. 
Cinnamene,  334. 
Cinnamic  aldehyde,  3^5. 
Coal,  79. 

gas,  82. 

oil,  79- 

tar,  82. 

tar  colors,  332. 
Cobalt,  273. 

salts  of,  274. 
Cobalticyanides,  294. 
Cocoa,  340. 
Codeine,  340. 
Coffee,  339. 
Coinage,  198. 
Coke,  79. 
Collodion,  328. 
Colloid,  171. 
Columbium,  252. 
Combination,  by  volume,  99. 

chemical,  3. 
Combining  weights,  68. 
Combustion,  26. 
Compounds,  9. 
Compound  blow-pipe,  34. 


Compound  radicles,  97. 
Coniferine,  343. 
Coniferyl  alcohol,  343. 
Conine,  339. 
Copper,  275. 

acetate,  306. 

compounds  in  general,  277. 

formate,  4. 

pyrites,  275. 

sulphide,  23. 
Copperas,  270. 
Coral,  206. 

Corrosive  sublimate,  230. 
Corundum,  233. 
Cream  of  tartar,  314. 
Crith,  19,  72. 
Cryolite,  III,  185,  235. 
Crystallization  from  fusion,  134. 

water  of,  48,  165. 
Crystalloid,  171. 
Cupellation,  198. 
Cuprammonium,  278. 
Cuprous  compounds,  277. 
Cyanides,  97,  291. 
Cyanogen,  97,  291. 

chlorides,  294. 

Davy's  safety-lamp,  89. 
Decane,  296. 
Decomposition,  4. 
Definite  proportions,  62. 
Deliquescence,  48. 
Density  of  gases,  TOO. 

of  solids  and  liquids,  44. 
Dextrin,  327. 
Dextrose,  325. 
Dialysis,  170. 
Diamond,  75. 
Didymium,  327. 
Dinitrobenzene,  331. 
Direct- vision  spectroscope,  217. 
Disinfectants,  77,  117,  123,  138. 
Dissociation,  194. 
Distillation,  46. 

fractional,  299. 
Dolomite,  223. 

Double  decomposition,  4,  200,  231. 
Dulong  and  Petit's  law,  259. 
Dynamite,  320. 

Efflorescence,  48. 
Electrochemical  series,  176. 


INDEX. 


365 


Electrolysis,  36,  174. 
Electroplating,  203. 
Electrotype,  277. 
Elements,  nature  of,  221. 

table  of,  9. 

Emerald,  169,  222,  233. 
Emery,  233. 
Emulsion,  342. 
Erbium,  237. 
Erythrite,  316. 
Ether,  301. 
Ethers,  mixed,  301. 
Ethyl,  alcohol,  298. 

butyrate,  306. 

oxide,  301. 
Ethylene,  81. 

Fats,  318. 
Fatty  acids,  303. 
Feldspar,  169,  236. 
Fermentation,  347. 
Ferric  compounds,  271. 
Ferrous  compounds,  270. 
Fibrin,  345. 
Filtration,  45. 
Fire-clay,  236. 
Firedamp,  80. 
Flame,  84. 
Flint,  168. 
Fluorescence,  341. 
Fluorine,  in. 
Fluor-spar,  112. 
Force,  5. 
Formulae,  chemical,  70. 

structural,  107. 
Fractional  distillation,  299. 
Fraunhofer's  lines,  218. 
Fraxin,  343. 
Fruit-ethers,  306. 
Fusel-oil,  300. 
Fusible  alloys,  250. 

Galena,  242. 
Gallium,  237. 
Galvanized  ironr  226. 
Garnet,  169. 
Gas,  illuminating,  82. 

laughing,  63. 
Gas  calculations,  21. 
Gas-carbon,  76. 
Gases,  condensation  of,  22. 

expansion  of,  20. 


Gasoline,  297. 
Gastric  juice,  346. 
Gelatin,  346. 
German-silver,  226,  273. 
Glass,  169. 
Glucinunv,  222. 
Glucose,  325. 
Glucosides,  342. 
Glue,  346. 
Gluten,  346. 
Glycerin,  318. 
Glycols,  311. 
Gold,  280. 

chloride,  282. 
Granite,  169. 
Grape-sugar,  325. 
Graphite,  76. 
Green  vitriol,  270. 
Grotto  del  Cane,  95. 
Guarana,  339. 
Gum-arabic,  327. 
Gun-cotton,  327. 
Gunpowder,  common,  192. 
Gunpowder,  white,  125. 
Gypsum,  208. 

Haemoglobin,  345. 

Heat  and  chemical  change,  5. 

Heavy  spar,  21 1. 

Hematin,  345. 

Hematite,  264. 

Heptane,  296. 

Hexane,  296. 

Homologous  series,  287. 

Hornblende,  169. 

Hyacinth,  239. 

Hydraulic  lime,  206. 

Hydrocarbons,  79,  287. 

Hydrogen,  14. 

chloride,  118. 

fluoride,  112. 

oxides,  14. 
Hydroxyl,  148. 
Hyoscyamine,  341. 

Ice,  43. 

Ice-machines,  58. 
Iceland-spar,  207. 
Illuminating  gas,  82. 
Indigo,  335. 
Indium,  237. 
Ink,  270,  343. 


366 


INDEX. 


Ink,  india,  77. 

printer's,  77. 
Iodine,  128. 

pentoxide,  130. 
lodoform,  302. 
Indium,  284. 
Iron,  264. 

oxides,  270,  271. 

pyrites,  271. 

salts  of,  270. 

scale,  271. 

sulphide,  270. 
Isomerism,  289. 

Kaolin,  236. 
Kerosene,  297. 
Ketones,  309. 

Labarraque's  solution,  123. 
Lac-sulphur,  134. 
Lactose,  324. 
Lamp,  safety,  89. 

spirit,  86. 
Lamp-black,  77. 
Lanthanum,  237. 
Lapis-lazuli,  235. 
Laurite,  282. 
Law,  of  Avogadro,  103. 

of  Boyle  and  Mariotte,  22. 

of  definite  proportions,  62. 

of  Dulong  and  Petit,  258. 

of  multiple  proportions,  62. 

two-volume,  100. 
Laws,  Berthollet's,  200. 
Lead,  241. 

acetate,  306. 

chromate,  256. 

salts  of,  in  general,  243,  244. 
Lead-chamber  crystals,  147. 
Lead-tree,  245. 
Leather,  343. 
Legumin,  346. 
Lepidolite,  184. 
Levulose,  325. 
Lime,  206. 
Lime-light,  35. 
Lime-water,  91. 
Limonite,  264. 
Litharge,  244. 
Lithium,  184. 

Madder,  336. 
Magenta,  332. 


Magnesia,  223,  224. 
Magnesite,  224. 
Magnesium,  223. 

compounds  of,  223,  224. 
Magnetite,  264. 
Malachite,  275. 
Manganese,  262. 

oxides,  262,  263. 

salts  of,  262,  263. 
Manganite,  262. 
Mannite,  316. 
Margarin,  319. 
Marsh-gas,  79. 

Marsh's  test  for  arsenic,  161. 
Matter,  5. 

Melissyl  alcohol,  300. 
Melting-point  table,  173. 
Mendelejeff's    classification,    180, 

181. 

Mercaptans,  301. 
Mercury,  228. 

oxides,  229. 

salts  of,  230. 
Metals,  10,  172. 
Methane,  79. 
Methane  series,  296. 
Methyl,  alcohol,  298. 

chloride,  302. 

salicylate,  333. 
Methylbenzene,  334. 
Mica,  169. 
Milk,  345. 
Minium,  244. 
Molecular  weight,  71. 
Molecule,  II,  12. 
Molybdenum,  257. 
Morphine,  340. 
Mortar,  207. 
Mouth  blow-pipe,  86. 
Multiple  proportion,  62. 

Naphtha,  297. 
Naphthalene,  336. 
Naphthalene-yellow,  336. 
Narcotine,  340. 
Nascent  state,  199. 
Nature  of  the  elements,  221. 
Nebular  hypothesis,  221. 
Nickel,  273. 

compounds  of,  274. 
Nicotine,  339. 
Niobium,  252. 


INDEX. 


367 


Nitrates,  58. 
Niter,  191. 
Nitrobenzene,  331. 
Nitrocellulose,  327. 
Nitrogen,  49. 

bromide,  128. 

chloride,  127. 

iodide,  130. 

oxides,  62-64. 
Nitroglycerin,  320. 
Nitrosyl  chloride,  121. 
Nitrotoluene,  334. 
Non-metals,  10. 
Nux  vomica,  341. 

Oils,  essential,  338. 

fatty,  318. 
defines,  310. 
Olein,  319. 
Onyx,  168. 
Opal,  168. 
Opium,  340. 
Orpiment,  163. 
Osmium,  284. 
Oxygen,  24. 

Oxyhydrogen  blow-pipe,  34. 
Ozone,  29,  104. 

Palladium,  284. 
Palmitin,  319. 
Paraffin,  296. 
Paris-green,  161. 
Pectin,  327. 
Pentane,  297. 
Pepsin,  346. 
Peptones,  346. 
Perissads,  157. 
Peruvian  bark,  340. 
Petroleum,  79,  297. 
Phenol,  330. 
Phenyl,  331. 
Phenylamine,  331. 
Phenylethylene,  334. 
Phloridzin,  343. 
Phosphates,  156. 
Phosphine,  154,  289. 
Phosphorus,  151. 

chlorides,  157. 

hydrides,  154. 

oxides,  155. 

oxychloride,  158. 
Photography,  201. 


Photolithography,  256. 
Plant-respiration,  97. 
Plaster,  207. 
Plaster  of  Paris,  209. 
Platinocyanides,  294. 
Platinum,  282. 

chloride,  283. 
Plumbago,  7°- 
Polymerism,  290. 
Populin,  343. 
Porcelain,  236. 
Porcelain-glass,  235. 
Potash,  190. 
Potassium,  183,  189. 

bicarbonate,  191. 

bromide,  191. 

carbonate,  190. 

chlorate,  124,  191. 

chloride,  191. 

chloroplatinate,  283. 

chromates,  255. 

cyanide,  292. 

ferricyanide,  293. 

ferrocyanide,  292. 

hydroxide,  190. 

iodide,  191. 

nitrate,  191. 

oxides,  190. 

perchlorate,  127. 

permanganate,  264. 

silicate,  169. 

sulphocyanate,  294. 

tartrates,  314. 
Pottery,  236. 

Pressure,  effect  on  gases,  22. 
Propane,  296. 
Propyl  alcohol,  300. 
Prussian  blue,  293. 
Puddling,  265. 
Purpurin,  336. 
Putrefaction,  347. 
Pyridine,  341. 
Pyrolusite,  262. 
Pyrotechny,  210. 
Pyroxylin,  327. 

Quantivalence,  105. 
Quartation,  280. 
Quartz,  168. 
Quicklime,  206. 
Quicksilver,  228. 
Quinine,  340. 


368 


INDEX. 


Realgar,  162. 
Red-lead,  244. 
Respiration,  28. 
Reversal  of  sodium-line,  219. 
Rhodium,  284. 
Rinmann's  green,  274. 
Rochelle  salt,  314. 
Rock-crystal,  168. 
Rosanilin,  332. 
Rosin,  338. 
Rubidium,  184,  217. 
Ruby,  233. 
Ruthenium,  284. 

Safety-lamp,  89. 
Salicin,  342. 
Salicyl  aldehyde,  333. 
Saligenin,  342. 
Sal-soda,  187. 
Salt,  common,  185. 
Salt-cake,  187. 
Saltpeter,  191. 
Salts,  defined,  61. 
Samarium,  238. 
Sand,  168. 
Sapphire,  233. 
Saratoga  water,  45. 
Scales,  thermometric,  42. 
Scandium,  237. 
Seidlitz-powder,  314. 
Selenite,  208. 
Selenium,  149. 
Serpentine,  223. 
Silica,  168. 
Silicates,  169. 
Silicon,  166. 

compounds  of,  167. 
Silver,  196. 

bromide,  201. 

chloride,  199. 

cyanide,  203,  292. 

iodide,  201. 

nitrate,  199,  202. 

oxide,  198. 

sulphate,  198. 

sulphide,  198. 
Silver-plating,  203. 
Slate,  169. 
Smelling-salts,  195. 
Smithsonite,  225. 
Smoke-consumers,  88. 
Snow,  43. 


Soap,  186,  319. 
Soda,  186. 
Sodium,  183. 

acetate,  306. 

bicarbonate,  189. 

borate,  165. 

carbonate,  186. 

chlorate,  125. 

chloride,  185. 

hydrogen  sulphite,  140. 

hydroxide,  186. 

hypochlorite,  123. 

hyposulphite,  141. 

nitrate,  189. 

oxides,  1 86. 

phosphate,  189. 

salicylate,  333. 

silicate,  169. 

stannate,  241. 

sulphate,  189. 

thiosulphate,  141. 

tungstate,  258. 

uranate,  258. 
Solanine,  341. 
Solder,  240. 
Solution,  44. 
Sombrerite,  151. 
Spathic  iron-ore,  264. 
Specific  gravity,  44. 

table  of,  173. 
Specific  heat,  259. 
Spectrometer,  215. 
Spectroscope,  214,  216. 
Spectrum,  absorption,  218. 

bright  line,  218. 

continuous,  218. 

nebular,  220. 

solar,  220. 

stellar,  220. 

Spectrum  analysis,  213. 
Spelter,  225. 
Spermaceti,  300. 
Spiegeleisen,  267. 
Spirit-lamp,  86. 
Spirits  of  wine,  300. 
Stalactite  and  stalagmite,  208. 
Starch,  326. 
Steam,  42. 
Stearin,  319. 
Steel,  268. 
Stibines,  289. 
Stibnite,  249. 


INDEX. 


369 


Stoichiometry,  73.                                 Toluidine,  334. 

Strontium,  205. 

Topaz,  169,  233. 

salts  of,  210. 

Trap,  169. 

Structural  formulae,  107. 

Trinitrophenol,  331. 

Strychnine,  341. 

Tungsten,  257. 

Substitution  compounds,  288. 

Turpentine,  338. 

Sucrose,  323. 

Turquoise,  235. 

Sugar,  cane,  323. 

Type-metal,  248. 

fruit,  325. 

• 

grape,  325. 

Ultramarine,  235. 

milk,  324. 

Unsaturated  compounds,  108. 

Sugar  of  lead,  306. 

Uranium,  258. 

Saint,  190. 

Urea,  294. 

Sulphocarbamide,  295. 
Sulphocarbonyl,  295. 
Sulpho-salts,  163. 
Sulphourea,  295. 
Sulphur,  132. 

Valency,  105,  157. 
Vanadium,  247. 
Vanilline,  343. 
Venetian  red,  271. 

acids  of,  141. 

Verdigris,  306. 

chloride,  148. 

Vermilion,  229. 

oxides,  138. 

Vinegar,  305. 

Sulphuretted  hydrogen,  136. 

Vitriol,  blue,  277. 

Sulphuryl  chloride,  148. 

green,  270. 

Superphosphates,  210. 

oil  of,  142. 

Syenite,  169. 

white,  227. 

Symbols  of  the  elements,  9,  66. 
Synthesis,  8. 

Water,  32. 
hard,  45. 

Trtl  —        nr*n 

mineral,  45. 

i  ale,  223. 
Tannin,  343. 
Tantalum,  252. 

of  constitution,  224. 
of  crystallization,  48,  165,  224. 

Tartar,  314. 

rain,  45. 

Tartar-emetic,  315. 

sea,  45. 

Tea,  339. 
Tellurium,  150. 
Terbium,  237. 
Terpenes,  338. 
Thallium,  203. 
Thebaine,  340. 
Thenard's  blue,  274. 
Theobromine,  340. 

soft,  45' 
Water-glass,  169. 
White-lead,  244. 
White-vitriol,  227. 
Williamson's  blue,  293. 
Wolfram,  257. 
Wood-spirit,  298. 
Wrought-iron,  265. 

Thermometric  scales,  42. 

Ytterbium,  237. 

Thorium,  239. 
Tin,  239. 

Yttrium,  237. 

compounds  of,  240,  241. 

Zinc,  225. 

Tin-plate,  240. 

compounds  of,  226,  227. 

Tinstone,  239. 

granulated,  15,  226. 

Titanium,  239. 

Zincite,  225. 

Tobacco,  339. 

Zircon,  239. 

Toluene,  334. 

Zirconium,  239. 

VALUABLE  BOOKS  RELATING  TO  CHEMISTRY. 


ARMSTRONG  (PROFESSOR  H.  E.)  Introduction  to  the  Study  of  Organic  Chem. 
istry.  12mo.  Cloth,  $1.50. 

COOKE  (PROFESSOR  JOSIAH  PARSONS,  JR.,  of  Harvard  University).  The 
New  Chemistry.  12ino.  Cloth,  $2.00. 

HOFFMANN  (FREDERICK).  Manual  of  Chemical  Analyeisfas  applied  to  the 
Examination  of  Medicinal  Chemicals.  A  Guide  for  the  Determination  of 
their  Identity  and  Quality,  and  for  the  Detection  of  Impurities  and  Adul 
terations,  For  the  Use  of  Pharmaceutists,  Physicians,  Druggists,  and 
Manufacturing  Chemists,  and  Students.  Cloth,  $3.00. 

JOHNSTON  (PROFESSOR  JAMES  F.  W.)  The  Chemistry  of  Common  Life.  A 
new  edition,  revised,-  enlarged,  and  brought  down  to  the  Present  Time. 
By  ARTHUR  HEKHERT  CHURCH,  M.  A.,  Oxon  ,  author  of  "  Food  :  its  Sources, 
Constituents  and  Uses."  Illustrated  with  Maps  and  numerous  Engravings 
on  Wood.  12mo.  Cloth,  $2.00. 

MILLER  (W.  ALLEN").  Introduction  to  the  Study  of  Inorganic  Chemistry. 
With  71  Figures  on  Wood.  12ino.  Cloth,  $1.50. 

RAINS  (GEORGE  W.,  M.D.)  Chemical  Exercises  in  Qualitative  Analysis,  for 
Ordinary  Schools.  By  GEORGE  W.  KAINS,  M.  D.,  Professor  of  Chemistry 
and  Pharmacy  in  the  Medical  Department  of  the  University  of  Georgia, 
etc.  Clotb,  flexible,  50  cents. 

ROSCOE  AND  SCHORLEMMER.    Treatise  on  Chemistry.    By  H.  E.  ROSCOE, 
F.  R.  S.,  and  C.  SCHORLEMMER.  F.R.  S.,  Professors  of  Chemistry  iu  the 
Victoria  University,  Owens  College,  Manchester.    Illustrated. 
INORGANIC  CHEMISTRY.    8vo.    Cloth.    Vol.  I,  Non-Metallic  Elements,  $5.00; 

Vol.  II,  Part  I,  Metals,  $3.00;  Vol.  II,  Part  II,  Metals,  $3.00. 
ORGANIC  CHEMISTRY.    8vo.    Clcth.    Vol.  Ill,  Part  I,  The  Chemistry  of  the 
Hydrocarbons  and  their  Derivatives,  $5.00;  Vol.  Ill,  Part  II.    Completing 
the  Work.    (In  preparation.) 

STRECKER  AND  WISLICENUS.  Short  Text-book  of  Organic  Chemistry. 
Translated  and  edited,  with  extensive  Additions,  by  W.  R.  HODGKINSON, 
Ph.  D.  ( Wurzburg),  and  A.  J.  GREENAWAY,  F.  I.  C.,  F.  C.  S.  Small  8vo. 

THORPE  AND  MUIR.  Qualitative  Chemical  Analysis  and  Laboratory  Practice. 
12rno.  Cloth,  $1.50. 

TILDEN  (W.  A.,  F.C.S.)  Introduction  to  the  Study  of  Chemical  Philosophy. 
12mo.  Cloth,  $1.50. 

VOGEL  (DR.  HERMANN).  The  Chemistry  of  Light  and  Photography.  With 
100  Illustrations.  12mo.  Cloth,  $2.00. 

WAGNER  (RUDOLF).  Hand-book  of  Chemical  Technology.  Translated  and 
edited,  from  the  eighth  German  edition,  with  extensive  Additions,  by 
WILLIAM  CROOKES,  F.  R.  S.  With  336  Illustrations.  8vo.  Cloth,  $5.00. 

YOUMANS  ^PROFESSOR  E.  L.)  Class-book  of  Chemistry.  New  edition.  I2mo. 
Cloth,  $1.50. 


New  York :  D.  APPLETON  &  CO.,  1,  3,  &  5  Bond  Street. 


Scientific  Publications. 


MAN  BEFORE  METALS.  By  N.  JOLY,  Professor  at  the  Science  Faculty 
of  Toulouse;  Correspondent  of  the  Institute.  With  148  Illustrations.  12mo. 
Cloth,  $1.75. 

"  The  discussion  of  man's  origin  and  early  history,  by  Professor  De  Quatrefages, 
formed  one  of  the  most  useful  volumes  in  the  '  International  Scientific  Series,1  and 
the  same  collectidiis  now  further  enriched  by  a  popular  treatise  on  paleontology,  by 
M.  N.  Joly,  Professor  in  the  University  of  Toulouse.  The  title  of  the  book,  '  Man 
before  Metals,'  indicates  the  limitations  of  the  writer's  theme.  His  object  is  to  bring 
together  the  numerous  proofs,  collected  by  modern  research,  of  the  great  age  of  the 
human  race,  and  to  show  us  what  man  was,  in  respect  of  customs,  industries,  and 
moral  or  religious  ideas,  before  the  use  of  metals  was  known  to  him.'' — New  York 
Sun. 

"  An  interesting,  not  to  say  fascinating  volume."— New  York  Churchman. 

ANIMAL  INTELLIGENCE.    By  GEORGE  J.   ROMANES,  F.  R.  8.,  Zoological 

Secretary  of  the  Linnaean  Society,  etc.    12mo.    Cloth,  $1.75. 

"  My  object  in  the  work  as  a  whole  is  twofold  :  First,  I  have  thought  it  desirable 
that  there  should  be  something  resembling  a  text-book  of  the  facts  of  Comparative 
Psychology,  to  which  men  of  science,  and  also  metaphysicians,  may  turn  whenever 
they  have  occasion  to  acquaint  themselves  with  the  particular  level  of  intelligence 
to  which  this  or  that  species  of  animal  attains.  My  second  and  much  more  impor- 
tant object  is  that  of  considering  the  facts  of  animal  intelligence  in  their  relation  to  the 
theory  of  descent." — from  the  Preface. 

"  Unless  we  are  greatly  mistaken,  Mr.  Romanes's  work  will  take  its  place  as  one 
of  the  most  attractive  volumes  of  the  '  International  Scientific  Series.'  Some  persons 
may,  indeed,  be  disposed  to  say  that  it  is  too  attractive,  that  it  feeds  the  popular  taste 
for  the  curious  and  marvelous  without  supplying  any  commensurate  discipline  in 
exact  scientific  reflection ;  but  the  author  has,  we  think,  fully  justified  himself  in  his 
modest  preface.  The  resnlt  is  the  appearance  of  a  collection  of  facts  which  will  be  a 
real  boon  to  the  student  of  Comparative  Psychology  for  this  is  the  first  attempt  to 
present  systematically  well-assured  observations  on  the  mental  life  of  animals."— Sat- 
urday Review. 

"  The  author  believes  himself,  not  without  ample  cause,  to  have  completely  bridged 
the  supposed  gap  bet  ween  unstinct  and  reason  by  the  authentic  proofs  here  mar- 
shaled of  remarkable  intelligence  in  some  of  the  higher  animals.  It  is  the  seemingly 
conclusive  evidence  of  reasoning  powers  furnished  by  the  adaptation  of  means  to  ends 
in  cases  which  can  not  be  explained  on  the  theory  of  inherited  aptitude  or  habit." — 
New  York  Sun. 

THE  SCIENCE  OF  POLITICS.  By  SHELDON  AMOS,  M.  A.,  author  of  "  The 
Science  of  Law,"  etc.  12mo.  Cloth,  $1.75. 

"  To  the  political  student  and  the  practical  statesman  it  ought  to  be  of  great  value." 
— New  York  Herald. 

"  The  author  traces  the  subject  from  Plato  and  Aristotle  in  Greece,  and  Cicero  in 
Rome,  to  the  modern  schools  in  the  English  field,  not  slighting  the  teachings  of  the 
American  Revolution  or  the  lessons  of  the  French  Revolution  of  1798.  Forms  of  gov- 
ernment, political  terms,  the  relation  of  law.  written  and  unwritten,  to  the  subject,  a 
codification  from  Justinian  to  Napoleon  in  France  and  Field  in  America,  are  treated 
as  parts  of  the  subject  in  hand.  Necessarily  the  subjects  of  executive  and  legislative 
authority,  police,  liquor,  and  land  laws  are  considered,  and  the  question  ever  growing 
in  importance  in  all  countries,  the  relations  of  corporations  to  the  state."— New  York 
Observer. 

New  York:  D.  APPLETON  &  CO.,  1,  3,  &  6  Bond  Street. 


Scientific  Publications. 


ANTS,  BEES,  AND  WASPS.  A  Record  of  Observations  on  the  Habits  of  the 
Social  Hymenoptera.  By  Sir  JOHN  LUBBOCK,  Bart.,  M.  P.,  F.  E.  S.,  etc.,  author 
of  "  Origin  of  Civilization,  and  the  Primitive  Condition  of  Man, '  etc.,  etc.  With 
Colored  Plates.  12rno,  cloth,  $2.00. 

"  This  volume  contains  the  record  of  various  experiments  made  with  ants,  bees,  and 
wasps  during  the  last  ten  years,  with  a  view  to  test  their  mental  condition  and  powers 
of  sense.  The  principal  point  in  which  Sir  John's  mode  of  experiment  differs  from 
those  of  Huber,  Forel,  McCook,  and  others,  is  that  he  has  carefully  watched  and 
marked  particular  insects,  and  has  had  their  nests  under  observation  for  long  periods 
— one  of  his  ants'  nests  having  been  under  constant  inspection  ever  since  1874.  His 
observations  are  made  principally  upon  ants  because  they  show  more  power  and  flexi- 
bility of  mind;  and  the  value  of  his  studies  is  that  they  belong  to  the  department  of 
original  research." 

"  We  have  no  hesitation  in  saying  that  the  author  has  presented  us  with  the  most 
valuable  series  of  observations  on  a  special  subject  that  has  ever  been  produced,  charm- 
ingly written,  full  of  logical  deductions,  and,  when  we  consider  his  multitudinous  en- 
gagements, a  remarkable  illustration  of  economy  of  time.  As  a  contribution  to  insect 
psychology,  it  will  be  long  before  this  book  finds  a  parallel."— London  Athenaeum. 

DISEASES  OF  MEMORY  :  An  Essay  in  the  Positive  Psychology.  By  TH. 
KIBOT,  author  of  "  Heredity,"  etc.  Translated  from  the  French  by  William 
Huntington  Smith.  12mo,  cloth,  $1.50. 

"M.  Ribot  reduces  diseases  of  memory  to  law,  and  his  treatise  is  of  extraor- 
dinary interest." — Philadelphia  Press. 

"Not  merely  to  scientific,  but  to  all  thinking  men,  this  volume  will  prove 
intensely  interesting." — New  York  Observer. 

"M.  Ribot  has  bestowed  the  most  painstaking  attention  upon  his  theme, 
and  numerous  examples  of  the  conditions  considered  greatly  increase  the  value 
and  interest  ot  the  volume."— Philadelphia  North  American. 

"  To  the  general  reader  the  work  is  made  entertaining  by  many  illustrations 
connected  with  such  names  as  Linnaeus.  Newton,  Sir  Waiter  Scott,  Horace  Ver- 
net,  Gusiave  Dore,  and  many  others."— Harrisburg  Telegraph. 

"The  whole  subject  is  presented  with  a  Frenchman's  vivacity  of  style." — 
Providence  Journal. 

"It  is  not  too  much  to  say  that  in  no  single  work  have  so  many  curious 
eases  been  brought  together  and  interpreted  in  a  scientific  manner."— Boston 
Evening  Traveller. 

MYTH  AND  SCIENCE.    By  TITO  VIGNOLT.  ,12mo,  cloth,  price,  $1.50. 

"  His  book  is  ingenious ; '.  .  .  his  theory  of  how  science  gradually  differen- 
tiated from  and  conquered  myth  is  extremely  well  wrought  out,  and  is  probably  in 
essentials  correct."— Saturday  Review. 

"The  book  is  a  strong  one,  and  far  more  interesting  to  the  general  reader  than  its 
title  would  indicate.  The  learning,  the  acuteness,  the  strong  reasoning  power,  and  the 
scientific  spirit  of  the  author,  command  admiration.1" — New  York  Christian  Advocate. 

"An  attempt  made,  with  much  ability  and  no  small  measure  of  success,  to  trace  the 
origin  and  development  of  the  myth.  The  author  has  pursued  his  inquiry  with  much 
patience  and  ingenuity,  and  has  produced  a  very  readable  and  luminous  treatise.1'— 
Philadelphia  North  American. 

"  It  is  a  curious  if  not  startling  contribution  both  to  psychology  and  to  the  early 
history  of  man's  development.1' — New  York  World. 

For  sale  by  all  booksellers ;  or  sent  by  mail,  post-paid,  on  receipt  of  price. 
New  York :  D.  APPLETON  &  CO.,  1,  3,  &  6  Bond  Street 


Scientific  Publications. 


THE  BRAIN  AND  ITS  FUNCTIONS.  By  J.  LUTS,  Physician  to  the 
Hospice  de  la  Salpetriere.  With  Illustrations.  12mo.  Cloth,  $1.50. 

"No  living  physiologist  is  better  entitled  to  speak  with  authority  upon  the 
structure  and  functions  of  the  hrain  than  Dr.  Lays.  His  studies  on  the  anatomy 
of  the  nervous  system  are  acknowledged  to  be  the  fullest  and  most  systematic 
ever  undertaken.  Dr.  Luys  supports  his  conclusions  not  only  by  his  own  ana- 
tomical researches,  but  also  by  many  functional  observations  of  various  other 
physiologists,  including  of  course  Professor  Ferrier's  now  classical  experi- 
ments."— St.  James's  Gazette. 

"Dr.  Luys,  at  the  head  of  the  great  French  Insane  Asylum,  is  one  of  the  most 
eminent  and  successful  investigators  of  cerebral  science  now  living;  and  he  has 
given  unquestionably  the  clearest  and  most  interesting  brief  account  yet  made  of 
the  structure  and  operations  of  the  brain.  We  have  been  fascinated  by  this  vol- 
ume more  than  by  any  other  treatise  we  have  yet  seen  on  the  machinery  of  sen- 
sibility and  thought ;  and  we  have  been  instructed  not  only  by  much  that  is  new, 
but  by  many  sagacious  practical  hints*  such  as  it  is  well  for  everybody  to  under- 
stand."— The  Popular  Science  Monthly. 

THE  CONCEPTS  AND  THEORIES  OF  MODERN  PHYSICS.  By 

J.  B.  STALLO.    12mo.    Cloth,  $1.75. 

"  Judge  Stallo's  work  is  an  inquiry  into  the  validity  of  those  mechanical  con- 
ceptions of  the  universe  which  are  now  held  as  fundamental  in  physical  science. 
He  takes  up  the  leading  modern  doctrines  which  are  based  upon  this  mechanical 
conception,  such  as  the  atomic  constitution  of  matter,  the  kinetic  theory  of  gases, 
the  conservation  of  energy,  the  nebular  hypothesis,  and  other  views,  to  find  how 
much  stands  upon  solid  empirical  trround.  and  how  much  rests  upon  metaphys- 
ical speculation.  Since  the  appearance  of  Dr.  Draper's  '  Religion  and  Science,' 
no  book  has  been  published  in  the  country  calculated  to  make  so  deep  an  impres- 
sion on  thoughtful  and  educated  readers  as  this  volume.  .  .  .  The  range  and 
minuteness  of  the  author's  learning,  the  aruteness  of  his  reasoning,  and  the 
singular  precision  and  clearness  of  his  style,  are  qualities  which  very  seldom 
have  been  jointly  exhibited  in  a  scientific  treatise."— New  York  /Sun. 

THE  FORMATION  OF  VEGETABLE  MOULD,  THROUGH  THE 
ACTION.  OF  WORMS,  WITH  OBSERVATIONS  ON  THEIR 
HABITS.  By  CHARLES  DARWIN,  LL.  D.,  F.  R.  S.,  author  of  "On  the 
Origin  of  Species,"  etc.,  etc.  With  Illustrations.  12mo,  cloth.  Price,  $1.50. 

"  Mr.  Darwin's  little  volume  on  the  habits  and  instincts  of  earth-worms  is  no 
less  marked  than  the  earlier  or  more  elaborate  efforts  of  his  genius  by  freshness 
of  observation,  unfailing  power  of  interpreting  and  correlating  facts,  and  logical 
vigor  In  generalizing  upon  them.  The  main  purpose  of  the  work  is  to  point  out 
the  share  which  worms  have  taken  in  the  formation  of  the  layer  of  vegetable 
mould  which  covers  the  whole  surface  of  the  land  in  every  moderately  humid 
country.  All  lovers  of  nature  will  unite  in  thanking  Mr.  Darwin  for  the  new  and 
interesting  li<jht  he  has  thrown  upon  a  subject  e  o  long  overlooked,  yet  so  full  of 
interest  and  instruction,  as  the  structure  and  the  labors  of  the  earth-worm." — 
Saturday  Review. 

"  Respecting  worms  as  among  the  most  useful  portions  of  animate  nature, 
Dr.  Darwin  relates,  in  this  remarkable  book,  their  structure  and  habits,  the  part 
they  have  played  in  the  burial  of  ancient  buildings  and  the  denudation  of  the 
land,  in  the  disintegration  of  rocks,  the  preparation  of  soil  for  the  growth  of 
plants,  and  in  the  natural  history  of  the  world."— -Boston  Advertiser. 

D,  APPLETON  &  CO.,  Publishers, 

1.  3.  &  5  Bond  Street,  New  York. 


UNIVERSITY  OP.  CALIFORNIA  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


VI  61     I      9IW 

.AUG    1    J9U 


17 

APR   10  1944 


DE 


9   1916 


OCT  26^16 
DEC  20  1916 


11977, 


8KLCIR./1PR10  77 


JUL1 

SEP  30  I92S 


DEC  28 


30m-6,'14 


VB   17059 


